Debugging Cloud Foundry

At Mendix we use Cloud Foundry quite extensively. So I get to debug some apps in Cloud Foundry from time to time, and I have been keeping this post as a draft for ages. However, since it could also be useful for other people to have this overview, I will publish it today so that I can refer people to it.

If you are running an ancient Cloud Foundry with DEA (which you really shouldn't do), you can read this blogpost for how to enter a Warden container. I would advise to use $ ps -ef | grep warden/depot to identify your Warden Container instead of the proposed $ ps -ef | grep warden as you will get less noise. You can find the instances.json file easily on the Warden runner by using find /var/vcap -name instances.json, it will likely be in /var/vcap/data/dea_next/db/instances.json though.

For almost everything Cloud Foundry related, you will need the apps GUID, which you can obtain via: cf app APPNAME --guid or if you prefer the hard way, CF_TRACE=true cf app APPNAME | grep summary. One of the requests should be something like: GET /v2/apps/937992d7-5fbe-441f-858e-c704291eb127/summary HTTP/1.1. Your app GUID is 937992d7-5fbe-441f-858e-c704291eb127.

Once you have the app’s GUID, you can look in the file /var/vcap/data/dea_next/db/instances.json in the runner VM. This file contains the mapping of app instances to Warden containers. Look for the application_id and instance_index fields that match the app and instance you care about, then use the warden_container_path value in the same JSON hash.

Now, let's go back to the present. If you are running a recent Cloud Foundry you will have Diego with a Garden-runC backend (no, not Garden-Linux). A good start here is to read this page as it has excellent documentation already. Cloud Foundry also has documentation on this, which is located here. Again, you will need the app GUID, or you could do: cf curl /v2/apps/$(cf app APPNAME --guid)/stats | jq 'with_entries(.value = .value.stats.host)' (requires jq installed) or the harder way CF_TRACE=true cf app APPNAME | grep stats | grep -v GET | jq .\"0\".\"stats\".\"host\". You are welcome!