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Posts Tagged ‘DNS’

Web 2.0 application architecture Template

Application created for a Startup based in Chicago

The term ‘Load Balancer’ is quite self-explanatory, it balances the load on application servers behind it. There can be ‘n’ number of application servers behind the Load Balancer  (LB) which would not be directly facing the end users.

Read more…

Openstack Cloud Software

OpenStack : The Mission

“ To produce the ubiquitous Open Source Cloud Computing platform that will meet the needs of public and private cloud providers regardless of size, by being simple to implement and massively scalable.”

OpenStack is a collection of open source software projects that enterprises/service providers can use to setup and run their cloud compute and storage infrastructure.Rackspace and NASA are the key initial contributors to the stack. Rackspace contributed their “Cloud Files” platform (code) to power the Object Storage part of the OpenStack, while NASA contributed their “Nebula” platform (code) to power the Compute part. OpenStack consortium has managed to have more than 150 members including Canonical, Dell, Citrix etc.

There are 5 main service families under OpenStack

Nova         –   Compute Service

Swift         –    Storage Service

Glance      –    Imaging Service

Keystone  –    Identity Service

Horizon    –    UI Service

Open Stack Compute Infrastructure (Nova)

Nova is the Computing Fabric controller for the OpenStack Cloud. All activities needed to support the life cycle of instances within the OpenStack cloud are handled by Nova. This makes Nova a Management Platform that manages compute resources, networking, authorization, and scalability needs of the OpenStack cloud. But, Nova does not provide any virtualization capabilities by itself; instead, it uses libvirt API to interact with supported hypervisors. Nova exposes all its capabilities through a web services API that is compatible with the EC2 API of Amazon Web Services.

Functions and Features:

• Instance life cycle management

• Management of compute resources

• Networking and Authorization

• REST-based API

• Asynchronous eventually consistent communication

• Hypervisor agnostic : support for Xen, XenServer/XCP, KVM, UML, VMware vSphere and Hyper-V

OpenStack Storage Infrastructure (Swift)

Swift provides a distributed, eventually consistent virtual object store for OpenStack. It is analogous to Amazon Web Services – Simple Storage Service (S3). Swift is capable of storing billions of objects distributed across nodes. Swift has built-in redundancy and fail-over management and is capable of archiving and media streaming. It is extremely scalable in terms of both size (several petabytes) and capacity (number of objects).

Functions and Features

• Storage of large number of objects

• Storage of large sized objects

• Data Redundancy

• Archival capabilities – Work with large datasets

• Data container for virtual machines and cloud apps

• Media Streaming capabilities

• Secure storage of objects

• Backup and archival

• Extreme scalability

OpenStack Imaging Service (Glance)

OpenStack Imaging Service is a lookup and retrieval system for virtual machine images. It can be configured to use any one of the following storage backends:

• Local filesystem (default)

• OpenStack Object Store to store images

• S3 storage directly

• S3 storage with Object Store as the intermediate for S3 access.

• HTTP (read-only)

Functions and Features

• Provides imaging service

OpenStack Identity Service (Keystone)

Keystone provides identity and access policy services for all components in the OpenStack family. It implements it’s own REST based API (Identity API). It provides authentication and authorization for all components of OpenStack including (but not limited to) Swift, Glance, Nova. Authentication verifies that a request actually comes from who it says it does. Authorization is verifying whether the authenticated user has access to the services he/she is requesting for.

Keystone provides two ways of authentication. One is username/password based and the other is token based. Apart from that, keystone provides the following services:

• Token Service (that carries authorization information about an authenticated user)

• Catalog Service (that contains a list of available services at the users’ disposal)

• Policy Service (that let’s keystone manage access to specific services by specific users or groups).

Openstack Administrative Web-Interface (Horizon)

Horizon the web based dashboard can be used to manage /administer OpenStack services. It can be used to manage instances and images, create keypairs, attach volumes to instances, manipulate Swift containers etc. Apart from this, dashboard even gives the user access to instance console and can connect to an instance through VNC. Overall, Horizon

Features the following:

• Instance Management – Create or terminate instance, view console logs and connect through VNC, Attaching volumes, etc.

• Access and Security Management – Create security groups, manage keypairs, assign floating IPs, etc.

 • Flavor Management – Manage different flavors or instance virtual hardware templates.

 • Image Management – Edit or delete images.

 • View service catalog.

 • Manage users, quotas and usage for projects.

 • User Management – Create user, etc.

 • Volume Management – Creating Volumes and snapshots.

 • Object Store Manipulation – Create, delete containers and objects.

 • Downloading environment variables for a project.

INSTALLATING OPEN STACK

We can install open stack ESSEX very easily using StackGeek script. Login to your box and install git with apt-get. We’ll become root and do an update first.

sudo  su
apt-get update
apt-get install git

Now checkout the StackGeek scripts from Github:

git clone git://github.com/StackGeek/openstackgeek.git   
cd openstackgeek

Install the Base Scripts

Be sure to take a look at the scripts before you run them. Keep in mind the scripts will periodically prompt you for input, either for confirming installation of a package, or asking you for information for configuration.

Start the installation by running the first script:

./openstack_base_1.sh

When the script finishes you’ll see instructions for manually configuring your network. You can edit the interfaces file by doing a:

vim /etc/network/interfaces

Copy and paste the network code provided by the script into the file and then edit:

auto eth0 
iface eth0 inet static
  address 192.168.1.48		
  network 192.168.1.0		
  netmask 255.255.255.0
 broadcast 192.168.1.255
  gateway 192.168.1.124			
  dns-nameservers 8.8.8.8  
auto eth1

Change the settings for your network configuration and then restart networking and run the next script:

/etc/init.d/networking restart

Then run the second script :

./openstack_base_2.sh

After the second script finishes, you’ll need to set up a logical volume for Nova to use for creating snapshots and volumes. Nova is OpenStack’s compute controller process.

Here’s the output from the format and volume creation process:-

root@manager-System-Product-Name:/openstackgeek# fdisk /dev/sda
Device contains neither a valid DOS partition table,nor Sun,SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0xb39fe7af.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.

Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)

Command (m for help): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): p Partition number (1-4, default 1): 3  
First sector (2048-62914559, default 2048): 
 Using default value 2048 Last sector,(2048-62914559,default 62914559): 
Using default value 62914559 
Command (m for help): w The partition table has been altered! 
Calling ioctl() to re-read partition table. Syncing disks.
root@manager-System-Product-Name:/openstackgeek# pvcreate -ff /dev/sda3
 Physical volume "/dev/sda3" successfully created
root@manager-System-Product-Name:/openstackgeek# vgcreate nova-volumes /dev/sda3
 Volume group "nova-volumes" successfully created 

Note: Your device names may vary.

Installing MySql

The OpenStack components use MySQL for storing state information. Start the install script for MySQL by entering the following:

./openstack_mysql.sh

You’ll be prompted for a password used for each of the components to talk to MySQL:
Enter a password to be used for the OpenStack services
to talk to MySQL (users nova, glance, keystone): redhat
Note(Here “redhat” is the password given to nova,glance,keystone) 

During the installation process you will be prompted for a root password for MySQL. In our install example we use the same password, ‘redhat’. At the end of the MySQL install you’ll be prompted for your root password again.

mysql start/running, process 8796
################################################################################ 
Creating OpenStack databases and users. 
Use your database password when prompted. 
 Run './openstack_keystone.sh' when the script exits. 
################################################################################
Enter password:
After MySQL is running, you should be able to login with any of the OpenStack 
users and/or the root admin account by doing the following:

mysql -u root -predhat
mysql -u nova -predhat nova
mysql -u keystone -predhat keystone
mysql -u glance -predhat glance

Installing Keystone

Keystone is OpenStack’s identity manager. Start the install of Keystone by doing:

./openstack_keystone.sh

You’ll be prompted for a token, the password you entered for OpenStack’s services, and your email address. The email address is used to populate the user’s information in the database.

Enter a token for the OpenStack services to auth wth keystone: redhattoken 
Enter the password you used for the MySQL users (nova, glance, keystone):redhat 
Enter the email address for accounts(nova,glance,keystone):user@company.com
You should be able to query Keystone at this point. 
You’ll need to source the“stackrc” file before you talk to Keystone:
 . ./stackrc   
 keystone user-list    
 Keystone should return a list of users:
+----------------------------------+---------+------------------------+--------+
|                id                | enabled |         email          |  name  |
+----------------------------------+---------+------------------------+--------+
| b32b9017fb954eeeacb10bebf14aceb3 | True    | user@company.com       | demo   |
| bfcbaa1425ae4cd2b8ff1ddcf95c907a | True    | user@company.com       | glance |
| c1ca1604c38443f2856e3818c4ceb4d4 | True    | user@company.com       | nova   |
| dd183fe2daac436682e0550d3c339dde | True    | user@company.com       | admin  |
+----------------------------------+---------+------------------------+--------+

Installing Glance

Glance is OpenStack’s image manager. Start the install of Glance by doing:

./openstack_glance.sh

The script will download an Ubuntu 12.04 LTS cloud image from StackGeek’s S3 bucket.Once it’s done, you should be able to get a list of images:

glance index

Here’s the expected output:

ID              :- 71b8b5d5-a972-48b3-b940-98a74b85ed6a 
Name            :- Ubuntu 12.04 LTS
Disk Format     :- qcow2 
Container Format:- ovf 
Size            :- 226426880

Installing Nova

We’re almost done installing! The last component is the most important one as well. Nova is OpenStack’s compute and network manager. It’s responsible for starting instances, creating snapshots and volumes, and managing the network. Start the Nova install by doing:

./openstack_nova.sh

You’ll immediately be prompted for a few items, including your existing network interface’s IP address, the fixed network address, and the floating pool addresses:

######################################################
The IP address for eth0 is probably 192.168.1.48.
Keep in mind you need an eth1 for this to work.
######################################################
Enter the primary ethernet interface IP: 192.168.1.48
Enter the fixed network (eg. 10.0.2.32/27): 192.168.1.0/24
Enter the fixed starting IP (eg. 10.0.2.33): 192.168.1.1
############################################################################
The floating range can be a subset of your current network. 
Configure your DHCP server to block out the range before you choose it here. 
An example would be 10.0.1.224-255
############################################################################
Enter the floating network (eg. 10.0.1.224/27):  
Enter the floating netowrk size (eg. 32):

The fixed network is a set of IP addresses which will be local to the compute nodes. Think of these addresses as being held and routed internally inside any of the compute node instances.

The floating network is a pool of addresses which can be assigned to the instances you are running. For example, you could start a web server and map an external IP to it for serving a site on the Internet.


Finish Installing Nova

Nova should finish installing after you enter all the network information. When it’s done, you should be able to get a list of images from Glance via Nova:

 nova image-list

And get the expected output we saw earlier from Glance:

root@manager-System-Product-Name:/openstackgeek# nova image-list
+--------------------------------------+------------------+--------+--------+
|                  ID                  |       Name       | Status | Server |
+--------------------------------------+------------------+--------+--------+
| 71b8b5d5-a972-48b3-b940-98a74b85ed6a | Ubuntu 12.04 LTS | ACTIVE |        |
+--------------------------------------+------------------+--------+--------+

Installing Horizon

Horizon is the UI and dashboard controller for OpenStack. Install it by doing:

./openstack_horizon.sh

When it’s done installing, you’ll be given a URL to access the dashboard. 
You’ll be able to login with the user ‘admin’ 
and whatever you entered earlier for your password. 
If you’ve forgotten it, simply grep for it in your environment:

env |grep OS_PASSWORD

The URL will be : http://192.168.1.48

You can login the Openstack dashboard by the following credentials

USER : admin

PASSWORD : redhat

DKIM (Domain keys ) & SPF for domains

DKIM – the technology pioneered by Google is a major weapon against fighting spam. SPF is also another tool that helps us achieve the same goal. Here is the quick steps to enable both.

 

  1.  SPF aka Sender Policy Framework  uses the DNS TXT field

Example:

dig agileblaze.com txt

;; ANSWER SECTION:
agileblaze.com. 300 IN TXT "v=spf1 ip4:52.205.101.12 ip4:52.202.71.86 include:_spf.google.com ~all"
agileblaze.com. 300 IN TXT "google-site-verification=C2mB_M1y9wd9wo8jMdzqSQt-nYUo_oJhlNs4H8rM5u4"

 

Tools to verify SPF

 

http://www.kitterman.com/spf/validate.html

 

Checking to see if there is a valid SPF record.

Found v=spf1 record for agileblaze.com:
v=spf1 ip4:52.205.101.12 ip4:52.202.71.86 include:_spf.google.com ~all

evaluating…
SPF record passed validation test with pySPF (Python SPF library)!

Domain Keys – DKIM

 

Domain keys also can be added in the TXT field. Unlike SPF, domain keys uses cryptography infrastructure. We will have to add the txt field in the following format

<selector>._domainkey.domain.TLD

In this example we are using the following,

agileblaze._domainkey.agileblaze.com

 

Generation of the the keys and Verification can be done with http://dkimcore.org/tools/

Once the keys are ready, just add them to the DNS records and forget SPAM!

SSL for Tomcat on AWS EC2

To launch an AWS/EC2 instance, at first setting up a security group to specify what network traffic is allowed to reach the instance. Then select an AMI and launch an instance from it. And create a volume in the same zone of the instance and attach with it. Format the device and mount it to a directory. After that follow the steps to create SSL for Tomcat:

1. For the tomcat we need java, so create a directory to save the Java Binary file.

[shell] mkdir /usr/java
cd /usr/java [/shell]

2. Download jdk binary file (jdk-x-linux-ix.bin) here
Use URL http://www.oracle.com/technetwork/java/archive-139210.html

3. Execute the Binary file

[shell] /usr/java/jdk-x-linux-ix.bin [/shell]

Now we have the Java in our device. Then Download the Tomcat and install it followed by the instructions:-

1. Create a directory to save the tomcat

[shell] mkdir /usr/tomcat
cd /usr/tomcat [/shell]

2. Download tomcat source file (apache-tomcat-x.tar.gz) here
Use URL http://apache.hoxt.com/tomcat/tomcat-6/v6.0.32/bin/

3. Extract that file

[shell] tar -zxvf apache-tomcat-x.tar.gz [/shell]

4. Edit the catalina.sh file

[shell] vim /usr/tomcat/apache-tomcat-x/bin/catalina.sh [/shell]

[shell]

#** Add at the top **
JAVA_HOME=/usr/java/jdk1.x.x_x

[/shell]

save and exit
5. Start the tomcat

[shell] /usr/tomcat/apache-tomcat-x/bin/startup.sh [/shell]

6. We can see the logs by using the given command

[shell]tail -f /usr/tomcat/apache-tomcat-x/logs/catalina.out [/shell]

7. Take the browser and enter the URL http://localhost
Now we can see the tomcat index page

8. To stop the tomcat

[shell]/usr/tomcat/apache-tomcat-x/bin/shutdown.sh [/shell]

Now configure the SSL Certificate for tomcat. When you choose to activate SSL on your web server you will be prompted to complete a number of questions about the identity of your website and your company. Your web server then creates two cryptographic keys – a Private Key and a Public Key. The Public Key does not need to be secret and is placed into a Certificate Signing Request (CSR) – a data file also containing your details.

Create a self signed certificate authority (CA) and keystore.

1. Make a directory to hold the certs and keystore. This might be something like:

[shell] mkdir /usr/tomcat/ssl
cd /usr/tomcat/ssl [/shell]

2. Generate a private key for the server and remember it for the next steps

[shell]openssl genrsa -des3 -out server.key 1024[/shell]

Generating RSA private key, 1024 bit long modulus
…………………..++++++
…++++++
e is 65537 (0x10001)
Enter pass phrase for server.key:
Verifying – Enter pass phrase for server.key:

3. Generate a CSR (Certificate Signing Request). Give the data after executing this command

[shell]openssl req -new -key server.key -out server.csr[/shell]

Enter pass phrase for server.key:
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter ‘.’, the field will be left blank.
—–
Country Name (2 letter code) [GB]:
State or Province Name (full name) [Berkshire]:
Locality Name (eg, city) [Newbury]:
Organization Name (eg, company) [My Company Ltd]:
Organizational Unit Name (eg, section) []:
Common Name (eg, your name or your server’s hostname) []:
Email Address []:

Please enter the following ‘extra’ attributes
to be sent with your certificate request
A challenge password []:
An optional company name []:

4. Remove the passphrasse from the key

[shell]cp server.key server.key.org
openssl rsa -in server.key.org -out server.key[/shell]

Enter pass phrase for server.key.org:
writing RSA key

5. Generate the self signed certificate

[shell]openssl x509 -req -days 365 -in server.csr -signkey server.key -out server.crt[/shell]

Signature ok
subject=/C=GB/ST=Berkshire/L=Newbury/O=My Company Ltd
Getting Private key

You should then submit the CSR. During the SSL Certificate application process, the Certification Authority will validate your details and issue an SSL Certificate containing your details and allowing you to use SSL. Typically an SSL Certificate will contain your domain name, your company name, your address, your city, your state and your country. It will also contain the expiration date of the Certificate and details of the Certification Authority responsible for the issuance of the Certificate.

Create a certificate for tomcat and add both to the keystore

1. Change the path to ssl

[shell]cd /usr/tomcat/ssl[/shell]

2. Create a keypair for ‘tomcat’

[shell]keytool -genkey -alias tom -keyalg RSA -keystore tom.ks[/shell]

Enter keystore password:
Re-enter new password:
What is your first and last name?
[Unknown]:
What is the name of your organizational unit?
[Unknown]:
What is the name of your organization?
[Unknown]:
What is the name of your City or Locality?
[Unknown]:
What is the name of your State or Province?
[Unknown]:
What is the two-letter country code for this unit?
[Unknown]:

Is CN=Unknown, OU=Unknown, O=Unknown, L=Unknown, ST=Unknown, C=Unknown correct?
[no]: yes

Enter key password for <tom>
(RETURN if same as keystore password):
Re-enter new password:

3. Generate a CSR (Certificate Signing Request) for tomcat

[shell]keytool -keystore tom.ks -alias tom -certreq -file tom.csr[/shell]

Enter keystore password:

4. create unique serial number

[shell]echo 02 > serial.txt[/shell]

5. Sign the tomcat CSR

[shell]openssl x509 -CA server.crt -CAkey server.key -CAserial serial.txt -req -in tom.csr -out tom.cer -days 365[/shell]

Signature ok
subject=/C=Unknown/ST=Unknown/L=Unknown/O=Unknown/OU=Unknown/CN=Unknown
Getting CA Private Key

6. Import the server CA certificate into the keystore

[shell]keytool -import -alias serverCA -file server.crt -keystore tom.ks[/shell]

Enter keystore password:
Owner: O=My Company Ltd, L=Newbury, ST=Berkshire, C=GB
Issuer: O=My Company Ltd, L=Newbury, ST=Berkshire, C=GB
Serial number: ee13c90cb351968b
Valid from: Thu May 19 02:12:51 EDT 2011 until: Fri May 18 02:12:51 EDT 2012
Certificate fingerprints:
MD5: EE:F0:69:01:4D:D2:DA:A2:4E:88:EF:DC:A8:3F:A9:00
SHA1: 47:97:72:EF:30:02:F7:82:BE:CD:CA:F5:CE:4E:ED:89:73:23:4E:24
Signature algorithm name: SHA1withRSA
Version: 1
Trust this certificate? [no]: yes
Certificate was added to keystore

7. Add the tomcat certificate to the keystore

[shell]keytool -import -alias tom -file tom.cer -keystore tom.ks[/shell]

Enter keystore password:
Certificate reply was installed in keystore

To configure a secure (SSL) HTTP connector for Tomcat, verify that it is activated in the $TOMCAT_HOME/conf/server.xml file. Edit this file and add the following lines.

Tomcat configuration

1. Edit the given portion of tomcat configuretion file and change the port as 80

[shell]vim /usr/tomcat/apache-tomcat-6.0.13/conf/server.xml[/shell]

[shell]“””””” <Connector port=”8080″ protocol=”HTTP/1.1″
connectionTimeout=”20000″
redirectPort=”8443″ /> “”””””

<Connector port=”80″ protocol=”HTTP/1.1″
connectionTimeout=”20000″
redirectPort=”8443″ />

[/shell]

2. Add the given portion to server.xml and give your password in the password portion

[shell]

<Connector port=”443″ protocol=”HTTP/1.1″ SSLEnabled=”true”
maxThreads=”150″ scheme=”https” secure=”true”
keystoreFile=”tom.ks”
keystorePass=”password”
clientAuth=”false” sslProtocol=”TLS” />

[/shell]

When you start the Tomcat Your web server will match your issued SSL Certificate to your Private Key. Your web server will then be able to establish an encrypted link between the website and your customer’s web browser.

Start the tomcat with SSL Certificate

1. Restart tomcat

[shell]/usr/tomcat/apache-tomcat-6.0.13/bin/shutdown.sh
/usr/tomcat/apache-tomcat-6.0.13/bin/startup.sh[/shell]

2. Go to https://Public DNS name:443/

Then your browser shows a security issue. Click the Approve button. Then you can enter to the tomcat with your certificate. When a browser connects to a secure site it will retrieve the site’s SSL Certificate and check that it has not expired, it has been issued by a Certification Authority the browser trusts, and that it is being used by the website for which it has been issued. If it fails on any one of these checks the browser will display a warning to the end user letting them know that the site is not secured by SSL.

You are Done !!!

Simulating multiple IP-Camera with h.264 stream in Amazon EC2 using Wowza

When you are setting up a Wowza based streaming application which need to stream and record more than a thousand cameras, and in the testing stage you need to see how the system works by providing multiple H.264 camera streams. But, when you have only one camera for testing purposes, you cannot overload the camera by taking a thousand streams from it to test the application. And if the camera gives an MPEG-4 stream, Wowza is not going to play since H.264 is the only supported format by it. We did a workaround to overcome this situation in Amazon EC2. We launched a large wowza instance from paid AMI and installed VLC in it. Using VLC we transcoded the MPEG-4 video stream to H.264. Illustration given below
Simulating multiple=
vlc -vvv rtsp://camera.hostname:port/stream-name --sout "#transcode{venc=x264{keyint=60,profile=baseline,level=3.0,nocabac, qpmax=36,qpmin=10,me=hex,merange=24,subme=9,qcomp=0.6},vcodec=x264,vb=128,scale=1, width=640,height=480,acodec=mp4a,channels=1,fps=15,samplerate=4750} :rtp{dst=local.amazon.ip.ofwowzainstance,port-video=10000,port-audio=10002 ,sdp=file:///wowza-installation-dir/content/vlc.sdp}" -R -d

Next we added a username and password to file /usr/local/WowzaMediaServer/conf/admin.password so that we can access the stream manager. Then we had to start wowza server, access the stream manager using the url http://public-dns-name-of.instance:8086/streammanager/

After Login using the username and password mentioned in /usr/local/WowzaMediaServer/conf/admin.password. Click on “start receiving stream” under rtplive.

In the configuration window mentioned Application as rtplive/_definst_ , MediaCaster Type as rtp, and Stream Name as vlc.sdp and clicked “OK” to submit and stream to start. The RSTP url to access the stream was be rtsp://public-dns-name-of.instance:8086/rtplive/vlc.sdp and this give an H.264 stream which is equivalent to a stream from an H.264 camera. The advantage of this setup is you need not overload a single IP camera by taking 1000 streams as this single rtsp output can be used multiple times to simulate a multiple IP-Camera system and feed it as input to the wowza streaming infrastructure we are developing in Amazon EC2.

Deploying a load balanced e-commerce portal in Amazon EC2

Update: NFS should not be used as that will be a SPOF. One should use S3 or other object stores. An alternative could be multi-node GlusterFS if someone needs volumes shared across nodes.

When building an infrastructure for an eCommerce portal on Cloud, it is important to note that it should be available all the time, that it is fail safe with outages like the one we had recently in AWS EU and U.S. East Regions, survive Hardware failure or any other issues like bug in the system or deployment errors. We built an infrastructure on AWS Cloud that address all these issues with LAMP using various AWS Cloud services like EC2, S3, RDS, EBS etc. It is described in detail below:

 

Achieving High Availability & Fail over across Datacenters

Elastic Load Balancer (ELB)

The Elastic Loadbalancer ( ELB ) service provided by AWS tries to achieve the following:

(i) Spans across Datacenters: Loadbalance traffic across mulitple datacenters (AZ )thus providing high availability even if one datacenter goes down. So you should always make sure that when you launch instances under an ELB, you should launch it in different Availability zones. You can also launch instances in the same AZ but by default ELB will redirect request across multiple AZ in a Round Robin way.

(ii) Failover: ELB will periodically monitor the health of the instances and if any of the instance or monitored service ( e.g. Http ) goes down, ELB will stop redirecting requests to that instance and all the request will be redirected to the remaining number of instances registered under ELB. When the instance comes backup, it will again start redirecting requests to that instance.

(iii) Handling root domain ( apex / main domain ) and subdomains: ELB can loadbalance only those requests coming to alias / subdomain( www ). It cannot handle request coming to root domain. This is because when you configure DNS for enabling ELB, you can only set CNAME to ELB for subdomains. There are 2 reasons for this. One is when you configure ELB, you will only get a Public DNS name for the ELB like the following instead of a Public IP.

[bash]Test-1736333854.us-east-1.elb.amazonaws.com [/bash]

This is because AWS changes the Public IP of the ELB periodically for providing scalability for ELB itself. Another reason why you cannot redirect main domain request to ELB is that DNS protocol itself restricts the usage of CNAME or anything other than “A” record for a root domain. So you cannot CNAME root domain to ELB DNS name.

So for serving root domain requests with ELB , there are only work arounds like mentioned below:

a) We have to assign an elastic IP for an instance under ELB. But what if this instance goes down? Set heartbeat to switch EIP? This is a bit complicated setup as switching EIP to instances present across AZ takes time.

b)The other option is to have the root domain point to the IP addresses of the destination by configuring one or more “A” records (address records) for root domain. You can do that if you know the destination IP addresses are fixed, such as if you are using EC2 Elastic IP addresses. We wouldn’t recommend this because IP addresses will be cached at the client end for long time even if you set low value of TTL at the nameservers. This is because TTL value can also be configured at the the client end overriding the TTL value provided by the nameserver of the domain. e.g. with nscd ( Nameserver Caching Daemon) you can set the TTL value manually in its configuration file.

c) You can keep a separate web server not under ELB with a Redirect Rule for redirecting root domain requests to www. You should make sure that this webserver is highly available as well.

d) A better solution is to go for Domain Registrars ( DNS service providers ) who provide this feature of redirecting root domain requests to www. So this can be handled at the DNS itself. The DNS service provided by AWS “Route53” can be used for this ‘Zone apex’ ( root domain ) redirection.

(iv) SSL Termination

There is support for “SSL termination” in ELB which means you can use ELB to loadbalance HTTPS requests too. You just need to buy the SSL certificate and simply upload it to ELB. ELB will redirect all the HTTPS request to the backend servers. So you can make an eCommerce portal highly secure and highly available with ELB.

(v) Persistent Session

You can enable Sticky Session with ELB but the problem is users will be logged out if any of the instance / webserver goes down and ELB will redirect the subsequent requests from the same user to a different instance and it will prompt the user to login again. To tackle this there were few options we had considered –
a)You can either setup distributed failover memcached server or
b)You can use RDS for storing Session.

We went for RDS as our Session Management store since RDS is an excellent choice for Database Administration as well if you are using MySQL as the Database.

Your application must be configured to write session data to an RDS database. So when an instance / webserver goes down and when the ELB redirects the user request to a different instance, the user will not be asked to login again as all servers are reading session data from the same place that is RDS. The user won’t notice anything at all, even though they’ve now started talking to another server. We recommend using a Multi-AZ RDS instance and write session data into this. So if one of your EC2 instances goes down, the other instances will still have access to the RDS database, and likewise if an RDS zone goes down, Amazon fail this over to the second AZ internally, transparently to you and your application.

So the easiest and most reliable way to share sessions for failover on a multi-server environment is to use RDS, since Amazon handle the database layer’s failover for you.

So basically you can achieve two things by using RDS – Session management and Database Management.

 

AutoScaling

The Autoscaling service provided by AWS allows you to scale horizontally up / down with CPU usage, RAM, Disk I/O etc.

Ideally you should use a Base AMI with Autoscaling that will pull the required packages from a Centralized location like Chef Platform and code from the Version Control System or S3. You can write a startup script to run on instance bootup for this purpose. So when Autoscaling launches a new instance it will pull all the latest updated versions of the packages, code and also any other required custom configurations from a centralized location. This will also make it easier to manage all the configuration details, code updates from a centralized location using tools like Chef Platform, Version Control System or S3 respectively.

Apart from Centralised Configuration / Code management, the reason for using Base ami with Autoscaling is that it is not possible to change the ami configured with Autoscaling service dynamically.

 

Storage for Application Files

We came across lot of options for storing the application files. However you have to consider your priorities before you select a storage service for the code. Following are the points to consider for your application file storage system:

(i)Latency issues: All shared storage systems like NFS / GlusterFS / EBS / S3 etc have latency issues when compared to Instance store (Ephemeral Storage)

(ii)High availability: If you are using a shared storage service like NFS, it should never go down for the entire system to be available all the time.

(iii)Access to the code: How to get the latest code during incremental roll out of a new instance because if you are using a shared storage, it becomes difficult to gives access to the shared storage system when a new instance is launched

We went for instance store / ephemeral store that gives you better I/O performance. You can keep your own highly available SVN repository or go for publicly available Version Control Systems like GitHub. At the same time you can also keep a copy in S3 and sync to it whenever there is a code update. This will make it more redundant.

The problem with using shared storage service like NFS / GlusterFS with EBS / S3 is it becomes difficult to avoid single point failure for NFS / GlusterFS service. But if your site doesn’t have much hits and your priority becomes redundancy, you can go for mounting S3 as filesystem using tools like s3cmd and use that as a shared storage with NFS for multiple instance. The problem with S3 is that it is not intended to be used as a filesystem and there have been issues reported with speed and caching. Or you can use EBS volume for code storage if you have only a single instance serving the request. Even using NFS with EBS volumes ( with frequent snapshots to S3 ) gives better performance than using S3 as shared storage for files.

Not only does instance store gives you better performance, error rates very rare. with EBS volumes error rates are reported frequently. Recent outages with AWS EU & US East Regions shows that the down time was made worse due to increase in time taken to recover from EBS errors.

 

Code Deployment

For automating code deployment, you can configure deployment tools like Capistrano. This will become very handy when you have multiple servers to update simultaneously. Capistrano uses Ruby language and is built for Ruby code deployment but with little changes, you can automate deployment of PHP / Perl / Python / JAVA based application.

chef-deploy is another tool that comes with chef for automating code deployment. Continuous Integration tools like Hudson / Cruise Control are excellent tools when you want to automate the Build, Deployment, Test and Rollback process.

For code deployment, we follow a Release Management process where we keep a staging environment that is an exact replica of the production environment. We push code to the production environment only when it’s been completely tested in the staging environment and approved by the Release Manager. This will further reduce the errors / bugs / and downtime time caused due to the code release.

 

Database Server

We went for RDS across AZ for High availability. AWS will take care of Redundancy, Performance Optimisation, Scalability and Backup. You can avoid the hassle of managing a Database Server by using RDS. RDS is as an excellent distributed highly available Session Management System. You can also take regular backup from RDS and keep it in S3.

You can also use Master–Slave Replication setup instead of RDS. This is also a good option for achieving high availability for Database server. The challenging part will be to manually configure failover for both master and slave servers, achieving scalability with traffic, backup configuration and performance optimization with increasing load. With RDS, all these will be managed by AWS.

 

Log handling

Keep all the important logs like Application logs, Syslogs, SSH log etc in EBS volume. You can either schedule regular snapshots of these EBS volume to S3 or you can even sync these log files to an S3 bucket periodically using tools like s3sync.

 

Configuration Management

If you have more than one server or are planning to scale up in future or would like to automate a lot of administration / coding stuffs, you should definitely use one of the Open Source freely available Configuration Management tools like Chef / puppet / Cfengine

Chef is new and has default support for AWS / EC2. We use Chef extensively for managing our infrastructure in AWS. Chef provide a lot of readily available cookbooks ( recipes / roles ) for LAMP, JAVA app, Cassandra, Hadoop, Nagios etc which can be used readily ( or with minimum customization ) to automate the infrastructure setup and configuration. Chef also comes with a tool called Chef-deploy for automating deployment of code.

So using Chef along with tools like Hudson / Cruisecontrol, you can automate the entire setup from infrastructure setup to configuration management to building, deployment and testing of your application.

 

Performance

To improve performance you can implement the following:

(i)Use caching mechanisms like Memcache(DB scaling) / aiCache / Varnish.

(ii)CDN ( Content Delivery Network ) is a must if you want to provide better end-user response time. There are lot of CDN providers but we recommend AWS CloudFront or Akamai for serving static files and images. For start-up and small business, CDN might be costly but as your target audience grows larger and becomes more global, a CDN is necessary to achieve fast response times.

 

Monitoring & Alert

For monitoring, go for open source monitoring tools along with a SaaS based monitoring application.

(i)There are lot of free and open source option available in the market – Nagios, Zenoss,Zabbix etc. This can be automated with Chef in such a way that when a new server is launched in to the cluster, it will be automatically added to the Nagios list of monitored servers.

(ii)You can also use excellent SaaS based monitoring apps like Pingdom, mon.itor.us, site24x7.com etc for monitoring and alerting via email, SMS or Twitter.

(iii)Custom scripts or tools like Munin & Monit for monitoring and restarting services if it crashes.

 

Backup

You can keep copies of code in an S3 Bucket and sync it with tools like s3sync with every update. For DB Backup, in addition to automated RDS Backup, you can take periodical standard DB backups using mysqldump and store it in S3 bucket.You can also use EBS volumes for keeping replica of code and DB Backup with periodical snapshots to S3.

An important thing to note about S3 storage is it is only a Highly available Storage System. It is not backed up automatically. That means if you delete anything manually from s3, it will be forever gone unless you have manually backed it up with multiple copies in S3. So make sure that you have enough backups available in S3.

Quick start with Elastic Load Balancer (ELB ) on EC2

Elastic Load Balancing ( ELB ) is an AWS load balancer service that is readily available for users who have signed up for AWS EC2 and s3 services . ELB is configured to automatically distribute incoming application traffic across multiple Amazon EC2 instances . Recently AWS has announced support for ELB to the AWS Management Console which will give users a simple, point-and-click web interface to create and configure load balancers for the AWS EC2 instances .

Below are the simple steps to configure ELB for webserver from the command line . Read more…