Unix domain sockets for APM in libdd_opentracing

[cep21]

Hi,

I currently use unix domain sockets in my k8s setup because they are easier to safely share across containers than host ports. Some more information about them here. I also have them working for APM inside python and various dd-trace libraries. I would like to enable APM for my k8s nginx ingress controller. I believe it uses libdd_opentracing.so. If I configure the field agent_host to a unix domain socket will it "just work"? Any advice on using UDS + nginx via the libdd_opentracing.so integration?

Thanks!

[cep21]

I believe it will not work due to how the agent protocol is setup at https://github.com/DataDog/dd-opentracing-cpp/blob/master/src/agent_writer.cpp#L44

[cgilmour]

You're correct, it will not "just work".
The agent writer is implemented using libcurl, and that needs extra options set when using a unix domain socket as the transport instead of TCP.

[cep21]

Thanks for the update. Would support for unix domain sockets for APM be reasonable feature to track for libdd_opentracing.so?

[cgilmour]

Hi @cep21, this has been added and will ship in the next release.
To enable it, a few steps will be required:

• configure a volume mount for the agent daemonset. It will create the socket in this location
• add the DD_APM_RECEIVER_SOCKET environment variable to the agent, providing a path within the volume mount. Eg; if the mount path is /var/run/datadog-agent, then the variable should be set to /var/run/datadog-agent/trace-agent.socket
• put an identical volume mount on the ingress-controller's deployment
• add the DD_TRACE_AGENT_URL environment variable to that deployment, set to the same value as DD_APM_RECEIVER_SOCKET from the earlier step
• make sure that nginx will pass-through the environment variable using the directive env DD_APM_RECEIVER_SOCKET;. One way to set this is using the main snippet configuration.

[cep21]

I'm guessing I also have to wait for a release of the nginx controller that has the latest ddtrace library? Can you update when that happens (or do you know which release it should target?)