The routing strategies that are available to you depend on the load balancer that you choose to use. The following table lists some examples of routing strategies:

Routing connection that use HTTP protocols

To route HTTP traffic, the load balancer must be able to inspect the HTTP headers and extract session information.

Diffusion sets an HTTP cookie named session with a connection-specific ID specifically for this purpose. Your load balancer can use this cookie to maintain a table of client to server mappings.

The session cookie is flagged with HttpOnly, which prevents scripts accessing the cookie. The session cookie is not flagged with Secure, which prevents the cookie from being sent over non-secure connections.

Sample HTTP conversation, cookie highlighted:

POST /diffusion/ HTTP/1.1
Host: localhost:8080
Connection: keep-alive
Content-Length: 0
tt: 90
Origin: http://localhost:8080
User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/48.0.2564.82 Chrome/48.0.2564.82 Safari/537.36
m: 0
ty: B
v: 4
Content-Type: text/plain;charset=UTF-8
Accept: */*
Referer: http://localhost:8080/tools/DhtmlClient.html
Accept-Encoding: gzip, deflate
Accept-Language: en-GB,en-US;q=0.8,en;q=0.6

HTTP/1.1 200 OK
Set-Cookie: session=c04815df73a1646d-0000000000000000; HttpOnly
Access-Control-Allow-Origin:http://localhost:8080
Cache-Control:no-store, no-cache
Content-Type:text/plain; charset=UTF-8
Content-Length:41

4.100.4.c04815df73a1646d-0000000000000000

POST /diffusion/ HTTP/1.1
Host: localhost:8080
Connection: keep-alive
Content-Length: 0
Origin: http://localhost:8080
c: c04815df73a1646d-0000000000000000
User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Ubuntu Chromium/48.0.2564.82 Chrome/48.0.2564.82 Safari/537.36
m: 1
Content-Type: text/plain;charset=UTF-8
Accept: */*
Referer: http://localhost:8080/tools/DhtmlClient.html
Accept-Encoding: gzip, deflate
Accept-Language: en-GB,en-US;q=0.8,en;q=0.6
Cookie: session=c04815df73a1646d-0000000000000000

Diffusion uses a session ID for the cookie. This enables the load balancer to maintain a map of each session ID to its target Diffusion server.

Instead, you can disable the Diffusion cookie and configure the load balancer to set a cookie that identifies the target server instead of the session. While the overhead of transmitting a cookie is still present between client and load balancer, the identifier can be smaller because there are a smaller number of servers than client sessions. Load balancers that use the cookie to identify the Diffusion server can send less data down the wire and consume fewer resources.

If you want to configure your load balancer to inject its own cookie, you can disable this Diffusion cookie. To disable the Diffusion cookie, set the <disable-cookie> element in the WebServer.xml configuration file of your Diffusion to true.

Routing connections that use streaming protocols

Streaming protocols that open a single socket and remain connected until they are no longer required appear immune to requiring any special routing considerations. However, in the event that connection keep-alive is enabled to handle reconnections in case of temporary connection loss, it is important that the reconnection attempt is routed to the original server.

Without the ability to parse headers (and indeed, the absence of a session ID at all), the most common method for routing a streaming protocol such as WebSocket is to create a client/server mapping based on the IP addresses of the endpoints. This technique is generally referred to as Sticky-IP, and has the advantage of also working with HTTP transports, if required.

For F5^®'s Sticky IP, ensure that the Source Address Translation option is set to Auto Map.

Figure 1. Sticky-IP in F5 BIG-IP

The drawback of this approach is that multiple users masquerading behind a proxy or access point can have the same IP address, and all requests from clients with that IP address are routed to the same Diffusion instance. Load balancing still occurs, but some hosts might be unfairly loaded.