PHP Session Clustering

The high availability of your PHP application can be achieved by implementing PHP sessions clustering in the cloud. To successfully handle application server failover we create an environment with Memcached, several Apache servers, and an NGINX load balancer:

1. Log in to the  

2. Click the Create environment button

3. In the Environment topology window choose two or more servers you want to use (for example, two instances of Apache) and Memcached Node. Type the name of the environment and click Create.

How It Works:–  When each session request is completed, the session is sent to the Memcached node for backup.  This session remains available on the original application server and can be used for serving the next request. After the second request completion, the session is updated in Memcached.

If the original server fails, the next request is routed to another application server. The newly requested server is asked for the session it doesn’t know. So this new server will find the needed session in the Memcached Node. It is identified according to the ID that was appended to the sessionID while session creation. As a result, the server can fetch the session from the Memcached Node.

When the server answers the request, it also updates the session in the Memcached Node. Thus there is no interruption of the app caused by the original server failure – the failover is successfully handled.

At the same time, the NGINX load balancer is distributing traffic across the cluster containing HTTP resources. You can check the load balancing in the BitssCloud using different load balancing tools.

How to Configure:-

1. Navigate to your environment in the dashboard and click the Config button for Apache.

2. In the opened tab go to etc > php.ini

3. Add the next line to Dynamic Extensions:

extension=memcached.so

4. Make the changes in the [Session] block:

session.save_handler = memcached

session.save_path = “< server >:11211”
Note-

< server > states for Memcached IP or URL which you can find by clicking

Info

button for the Memcached node in your environment.

5. Save the changes and restart the Apache node.

That’s all! Now if one of the instances fails, the users get automatically switched to the other instance in this cluster and never notice any change.