iRule for host rewriting between nodes

Hello,

Have you tried replacing the event "LB_SELECTED" with "HTTP_REQUEST" in your iRule? 

According to the online docs:

HTTP::header and HTTP::host are not under the "LB_SELECTED" event, but

LB::server, HTTP::header and HTTP::host commands are available under HTTP_REQUEST 

Thanks,

Have you tried switching the event from LB_SELECTED to HTTP_REQUEST?  I don't believe the HTTP::Header or HTTP::Host commands are available under LB_SELECTED.

Yes, I have tested both events, but it seems that the fact that there is an SSL Profile Server makes the rewrite not behave correctly.
However, if I disable the SSL Profile Server it seems to be working correctly. It seems to be some incompatibility between my code and the existence of encryption F5 <> Nodes.

Hi Martin182 

What is the backend server application port? 

I have found another possible approach, using data groups combined with iRule. 

https://community.f5.com/discussions/technicalforum/rewrite-host-header-to-specific-pool-member/152235 

https://community.f5.com/discussions/technicalforum/change-host-header-for-each-node-in-a-pool/190532

I may try it out during the day.

Hi Martin,

You can try add logging statements to your iRule to capture the selected server and the rewritten Host header. This will help you verify that the iRule is executing as expected.

Adding logging can help debug the issue:

when LB_SELECTED {

    log local0. "Selected server: [LB::server addr], Host: [HTTP::host]"

    switch -glob [string tolower [HTTP::host]] {

        "service1.dns.com" {

            if { [LB::server addr] eq "192.168.50.100" } {

                log local0. "Rewriting Host to service1.ocp.site1.com"

                HTTP::header replace Host "service1.ocp.site1.com"

            } elseif { [LB::server addr] eq "192.168.50.101" } {

                log local0. "Rewriting Host to service1.ocp.site2.com"

                HTTP::header replace Host "service1.ocp.site2.com"

            }

        }

        "service2.dns.com" {

            if { [LB::server addr] eq "192.168.50.100" } {

                log local0. "Rewriting Host to service2.ocp.site1.com"

                HTTP::header replace Host "service2.ocp.site1.com"

            } elseif { [LB::server addr] eq "192.168.50.101" } {

                log local0. "Rewriting Host to service2.ocp.site2.com"

                HTTP::header replace Host "service2.ocp.site2.com"

            }

        }

        "service3.dns.com" {

            if { [LB::server addr] eq "192.168.50.100" } {

                log local0. "Rewriting Host to service3.ocp.site1.com"

                HTTP::header replace Host "service3.ocp.site1.com"

            } elseif { [LB::server addr] eq "192.168.50.101" } {

                log local0. "Rewriting Host to service3.ocp.site2.com"

                HTTP::header replace Host "service3.ocp.site2.com"

            }

        }

        "service4.dns.com" {

            if { [LB::server addr] eq "192.168.50.100" } {

                log local0. "Rewriting Host to service4.ocp.site1.com"

                HTTP::header replace Host "service4.ocp.site1.com"

            } elseif { [LB::server addr] eq "192.168.50.101" } {

                log local0. "Rewriting Host to service4.ocp.site2.com"

                HTTP::header replace Host "service4.ocp.site2.com"

            }

        }

    }

}

This will log the selected server and the host header, helping you verify if the conditions are being met and the headers are being rewritten correctly.

Use a tool like curl or a web browser to generate traffic to your virtual server. For example:

curl -H "Host: service1.dns.com" http://192.168.50.100

curl -H "Host: service2.dns.com" http://192.168.50.100

curl -H "Host: service3.dns.com" http://192.168.50.100

curl -H "Host: service4.dns.com" http://192.168.50.100

curl -H "Host: service1.dns.com" http://192.168.50.101

curl -H "Host: service2.dns.com" http://192.168.50.101

curl -H "Host: service3.dns.com" http://192.168.50.101

curl -H "Host: service4.dns.com" http://192.168.50.101

When you run the command curl -H "Host: service1.dns.com" http://192.168.1.100, you are making an HTTP request to the server at 192.168.50.100 and setting the Host header to service1.dns.com. This simulates a request as if it were coming from a client trying to access service1.dns.com, allowing you to test how your iRule handles this specific host.

Check Logs:

Review the logs on your F5 load balancer to verify that the iRule is executing correctly. Look for the log entries you added to confirm that the Host header is being rewritten as expected.

Ensure that the applications on OpenShift are receiving the correct Host headers and responding appropriately. Check for any 404 errors or other issues.

Monitor the traffic and logs to ensure the iRule continues to function correctly. Make any necessary adjustments based on your observations.

 Use tools like grep to filter and view specific log entries. For example:

grep "Selected server" /var/log/ltm

grep "Rewriting Host" /var/log/ltm

HTH

Best Regards

F5 Design Engineer