502 Bad Gateway Error

[ashish_solanki]

Hi All,

My app lication team is getting error 502 Bad Gateway when they try to access below URL:

For eg: www.xyz.com/lib/dict.en-US.json 

Below is the traffic flow.

Public --->>> DNS --> CDN ---> F5 --|||-> LB (10.x.x.x) ---> Apache servers (10.x.x.x1 & x2)

I have few policies on VIP which says if the request comes with above URI redirect it to a new pool.

I told app team 502 error is related to server only. Can someone hele here what things I can check on F5 to tshoot this issue.

Thanks,

[Daniel_Wolf]

Hi @ashish_solanki,

pity you have to prove your innocence here. My standard answer to such accusations usually is: "The BIG-IP does not send a HTML page unless it is configured to do so."

Before you make such a bold statement with confidence, you should check that your configuration on the BIG-IP is correct. You can do the following to further analyze the issue and to verify your config is working as intended:

• Try curl from the BIG-IP to /lib/dict.en-US.json on the Apache servers directly. Check that you get the correct response from the backend server.
• Capture traffic between BIG-IP and backend server with tcpdump. This should show that the 502 status page is sent by the web application server. And also this will verify that the request is arriving at the correct Apache servers. 
  If you are not experienced with tcpdump - start from here: K411: Overview of packet tracing with the tcpdump utility 
• Capture traffic going to the web application server when you access /lib/dict.en-US.json directly.
  Compare differences - maybe you find a solution in the differences.

Good luck,
Daniel