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_JOHN_'s avatar
Icon for Altocumulus rankAltocumulus
Dec 13, 2021

Change server SSL profile based on HTTP content

I have a single Virtual Server which provides internal to external access for a specific set of FQDNs (and nothing else).

It is a wildcard VS which accepts traffic destined to the actual external IPs. The VS does not perform destination IP/port translation (but source IP is SNATed) - i.e. traffic arrives at VS by:


  • Client does DNS lookup and gets external 'real' IP
  • Client establishes connection to this IP - but traffic actually directed to, and picked up by, F5 wildcard VS


VS has a pool with only 1 member, which is an upstream device that transports traffic to the internet (F5 basically uses pool member to get layer 2 MAC to forward the traffic to, but the layer 3 IP addressing of the traffic remains as that originally received, i.e. the actual external server IPs).

Each FQDN has its own specific Server SSL profile, which is assigned by iRule (based on client presented SNI).

This has all been working OK for a long time.


There is now a requirement that a couple of the FQDNs will need different server SSL profiles based on content within the HTTP request. It is possible that a single incoming TCP connection to the VS could contain HTTP requests which are to be handled differently, e.g.

HTTP Header X = A Server connection should use SSL profile A

HTTP Header X = B Server connection should use SSL profile B


The problem here is that you can't just set up a server connection based on the initial HTTP Header X received on a new clientside connection to the VS. It is posible that different HTTP requests could then come across that single client TCP stream each requiring a different Server SSL profile (choice of two, A or B).


My question is can anyone suggest how this can be accomplished without having to change anything on the clientside?


I have set something up which on first inspection appears to work in a 'lab' (i.e. PC running VMWare and LTM VE :-). I don't want to describe it just yet in case what I have done isn't the best solution (or maybe wouldn't even work properly in a real world setting with lots of load). At this point I am just looking for ideas of how other's might approach this, and don't want to influence anyone's ideas by describing my first attempt :-)


So any ideas??? Please ask any questions as needed to help clarify the ask :-)

6 Replies

  • The OneConnect profile allows you to load balance client http requests to server flows in a non 1-to-1 manner. While perhaps the traditional idea is multiple client connections reuse a single serverside connection, it also allows a single client connection to use multiple different serverside connections.


    • _JOHN_'s avatar
      Icon for Altocumulus rankAltocumulus

      Thank you very much for the reply. It would be good to use oneconnect if possible, but I am not sure how to make that happen yet 😊


      The lab setup I tried (please feel free to rubbish this setup and suggest any better alternatives) uses 1 pool per FQDN/HTTP combination. For example if I describe using just two pools for simplicity:


      -      { with Header X = A} maps to Pool A

      -      { with Header X = B} maps to Pool B


      I then used a traffic policy to forward traffic to the appropriate pool based on this FQDN/HTTP combination.


      Other than name, each pool is 100% the same – same single member (IP & port). The only reason I used different pools was to give different ‘targets’ to load balance to (very welcome to suggestions which only require 1 pool).


      I then used an iRule to pick up LB_SELECTED events and assign the appropriate Server SSL profile based on the name of the pool chosen, with the profile actually being attached and used in the subsequent SERVER_CONNECTED event.


      This appears to work OK, with a traffic profile along the lines of:


      -      { with Header X = A}

      first HTTP request received – create new server connection using server SSL profile A

      -      { with Header X = A}

      Any number of subsequent HTTP requests received with same FQDN/HTTP combination –LB_SELECTED doesn’t even trigger, traffic just goes across existing server connection OK

      -      { with Header X = B}

      HTTP request received with diff FQDN/HTTP combination – existing server connection closed (TCP FIN) and new connection established to same server but using server SSL profile B

      -      { with Header X = B}

      Again connection remains constant while subsequent HTTP requests present with the same FQDN/HTTP combination

      -     { with Header X = A}

      Cycle repeats…….



      At the TCP level the two server connections (A & B) will be the same, i.e. client addr/port & server add/port will be the same. However the key difference is that each will have used a different server SSL profile, i.e.

      Pool A connections use server SSL profile A

      Pool B connections use server SSL profile B


      Is the oneconnect TCP reuse pool aligned per LTM pool, or is it ‘global’? What is the relationship between TCP and SSL with regard to the idle connections in the reuse pool – i.e. are they purely TCP connections or do they also have active SSL sessions?


      I did try enabling oneconnect but results were inconsistent, although usually it just kept all traffic going across the first connection established. I therefore assumed the oneconnect reuse pool was global rather than being a separate reuse pool per LTM pool. I also assume SSL remains established per TCP connection.


      If you could help me understand how to amend the setup (happy to scrap what I have and go with something completely different) so as to leverage the power of oneconnect, but while still maintaining the key goal of ensuring the traffic is sent across a pipe which has used the correct server SSL profile it would be very much appreciated 😊


      Basically the ideal goal would be traffic switching between two different ‘SSL pipes’ to the same server, similar to that listed above, but with each connection remaining up rather than only one being activated at a time. I know the objective of oneconnect is to keep connections active like that, but I need to understand more about what a oneconnect idle connection actually represents and how the F5 makes a decision on which one to choose – e.g. if it is purely on IP/port info, or if there is some way I can align this to account for the different server SSL profiles used as well.

      • Josiah's avatar
        Icon for Employee rankEmployee

        Essentially the oneconnect profile is used IN ADDITION to what you have already configured in your irule/LTM profile. Without a oneconnect profile, your only option is to create a brand new serverside connection every time your header changes. With a oneconnect profile, you can have persistent serverside connections to your two destinations "kept open" and then, depending on the header in the client request, it will just send it to an available connection instead of creating a new one.


        That said, oneconnect is not going to pipeline multiple clients to a single server connection, it'll only use an existing connection if that connection is IDLE. If there are no IDLE serverside connections, it'll create a new one, similarly, if you don't meet the mask (for example a /32 mask means clients can only reuse their own connections, whereas a /24 you could let clients with source ips in the same subnet share connections with each other) criteria, it'll also create a new connection (even if there is an idle one for a different mask). The interaction of all this various logic probably explains what you observed as "inconsistent".


        It is definitely one of the stranger profiles to understand and tune, but it sounds to me like if you keep your current setup and just add a /32 oneconnect, and it has a timeout that is, say, about twice as long as what you would estimate as the average time between user requests with headers for DIFFERENT destinations, you'd probably see some performance gain.


        On the other hand, you can just create new connections every time like you are now, if you have the memory to spare. As long as your tcp idle timeout is reasonable and connections get culled regularly, the impact on the box isn't serious (although your users will obviously experience the delay of a tcp + tls handshake every time the headers switch)