Sticky Session¶
Sticky sessions ensure that requests from a client always get routed to the same backend server before a session elapses.
Here is an example that describes what sticky sessions. Assume that you have logged in to a server. After a while, you send another request. If sticky sessions are not enabled, the request may be routed to another server, and you will be asked to log in again. If sticky sessions are enabled, all your requests are processed by the same server, and you do not need to repeatedly log in.
Sticky sessions at Layer 4 are different from those at Layer 7.
Prerequisites¶
You have selected Weighted round robin for Load Balancing Algorithm.
Constraints and Limitations¶
If you use Direct Connect, VPN, or Cloud Connect connectionto access ELB, you must select Source IP hash as the load balancing algorithm and disable sticky sessions for ELB.
Differences Between Sticky Sessions at Layer 4 and Layer 7¶
OSI Layer | Listener's Protocol | Sticky Session Type | Stickiness Duration | Scenarios Where Sticky Sessions Become Invalid |
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Layer 4 | TCP or UDP | Source IP address: The source IP address of each request is calculated using the consistent hashing algorithm to obtain a unique hash key, and all backend servers are numbered. The system allocates the client to a particular server based on the generated key. This enables requests from different clients to be routed and ensures that a client is directed to the same server that it was using previously. |
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Layer 7 | HTTP or HTTPS |
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ELB supports three types of sticky sessions: Source IP address, Load balancer cookie, and Application cookie
Enabling Sticky Sessions¶
Log in to the management console.
In the upper left corner of the page, click and select the desired region and project.
Hover on in the upper left corner to display Service List and choose Network > Elastic Load Balancing.
Locate the load balancer and click its name.
Click Backend Server Groups, locate the backend server group, and click on the right of its name.
Enable Sticky Session, select the sticky session type, and set the session stickiness duration.
Click OK.
Note
You can also configure sticky sessions when adding a listener or creating a backend server group.