Commits on May 25, 2023

1. Fix the slow startup and termination of the vali-0 pod …

   The vali-0 pod takes more than a minute to start up and 30s to terminate
   eventually, "ungracefully". It turns out that this is the result of a few
   configuration issues.
   
   <details>
   <summary>Startup phase</summary>
   
   When vali starts up in the default configuration, it waits for 1 minute until it
   reports a ready status via its `/ready` endpoint. This is reproducible directly
   with the docker image:
   
   ```text
   docker run --rm -it -p 3100:3100 ghcr.io/credativ/vali:v2.2.5
   while true; do curl localhost:3100/ready; sleep 1; done
   Ingester not ready: waiting for 1m0s after startup
   ...
   ```
   
   > This is to work around race conditions with ingesters exiting and updating the
   > ring.
   
   https://github.com/credativ/vali/blob/d8985fc135e85518a5829b255afa7757d4714349/vendor/github.com/cortexproject/cortex/pkg/ring/lifecycler.go#L89
   
   The reasoning behind this default value is not applicable in the Gardener setup
   of vali. Vali is executed in "single binary mode", so there are no other
   ingester instances involved. Hence we can set this delay to a lower value.
   
   ```text
   docker run --rm --entrypoint sh ghcr.io/credativ/vali:v2.2.5 -c "cat /etc/vali/local-config.yaml" | sed '/lifecycler:/a \    min_ready_duration: 1s' > local-config.yaml
   docker run --rm -it -p 3100:3100 -v ./local-config.yaml:/etc/vali/local-config.yaml ghcr.io/credativ/vali:v2.2.5
   while true; do curl localhost:3100/ready; sleep 1; done
   Ingester not ready: waiting for 1s after startup
   ready
   ...
   ```
   
   Furthermore, the `initialDelaySeconds` setting of the readiness probe of vali is
   removed to let it default to 0s: even instances with significant amount of logs
   actually start up in less than 1s. There is no need to delay the initial
   readiness probe.
   
   </details>
   
   <details>
   <summary>Termination phase</summary>
   
   The `final-sleep` configuration parameter is changed to 0s from its default
   value of 30s. The default value of 30s meant that due to the same default 30s
   pod termination grace period, whenever vali was gracefully stopped (received a
   SIGTERM signal), it waited for 30(+epsilon)s until it would have shut down
   gracefully. However, shortly before that (after 30s), the kubelet sends a SIGKILL
   to forcefully stop the process: an undesired unclean shutdown, each and every
   time.
   
   The motivation of allowing for a final scrape of the exposed metrics before the
   shutdown is not relevant in the Gardener case, given that the Prometheus scrape
   interval is 1m anyways. So this commit changes the `final-sleep` configuration
   to 0s, which happens to be the default value in the "single binary mode".
   
   https://github.com/credativ/vali/blob/d8985fc135e85518a5829b255afa7757d4714349/vendor/github.com/cortexproject/cortex/pkg/ring/lifecycler.go#L90
   https://github.com/credativ/vali/blob/d8985fc135e85518a5829b255afa7757d4714349/cmd/vali/vali-local-config.yaml#L17
   
   Furthermore, the telegraf container of the vali-0 pod in the control plane
   namespace was not properly handling the SIGTERM signal: it was always killed by
   the kubelet after 30s with a SIGKILL. This was the other reason of the slow
   termination of the vali-0 pod. By letting bash execute the telegraf process in
   the background and waiting for it indefinitely with wait, the bash process with
   PID 1 can handle the SIGTERM signal that is sent by the kubelet. It sends a
   SIGTERM signal to its child bash process upon receiving a SIGTERM signal. This
   in turn handles the SIGTERM signal as well and sends it to its telegraf child
   process. Both bash processes wait for their child process to terminate. This way
   all the processes of the telegraf container terminate gracefully and in less
   than 1s when the SIGTERM signal is sent by the kubelet.
   
   Note that testing the signal propagation in the "minimized" telegraf image is
   tricky. On a linux based "local setup" where the "nested" docker&containerd
   containers are just regular processes of the host, the following approach can
   help to understand the signal propagation.
   
   Find the 3 processes of the telegraf container from the _host_:
   
   ```text
   ps aux | grep telegraf
   
   root 2483208 /bin/bash -c trap 'kill %1; wait' SIGTERM bash /etc/telegraf/start.sh & wait
   root 2483255 bash /etc/telegraf/start.sh
   root 2483260 /usr/bin/telegraf --config /etc/telegraf/telegraf.conf
   root 2494748 grep telegraf
   ```
   
   Attach strace to the 3 processes with `strace -p <pid>`. Send a SIGTERM signal
   to PID 1 with `k exec vali-0 -c telegraf -- bash -c "kill 1"` to check the
   signal propagation.
   
   </details>
   
   <details>
   <summary>With this change, the vali-0 pod starts up and terminates in less than 10
   seconds in the examples below.</summary>
   
   ```text
   k get pods vali-0 -w | ts
   
   17:25:09 vali-0   4/4     Terminating
   17:25:11 vali-0   4/4     Terminating
   17:25:11 vali-0   0/4     Terminating
   17:25:11 vali-0   0/4     Terminating
   17:25:11 vali-0   0/4     Terminating
   17:25:11 vali-0   0/4     Pending
   17:25:11 vali-0   0/4     Pending
   17:25:11 vali-0   0/4     Init:0/2
   17:25:12 vali-0   0/4     Init:0/2
   17:25:13 vali-0   0/4     Init:1/2
   17:25:14 vali-0   0/4     PodInitializing
   17:25:15 vali-0   3/4     Running
   17:25:16 vali-0   4/4     Running
   
   17:27:38 vali-0   2/2     Terminating
   17:27:41 vali-0   2/2     Terminating
   17:27:42 vali-0   0/2     Terminating
   17:27:42 vali-0   0/2     Terminating
   17:27:42 vali-0   0/2     Terminating
   17:27:42 vali-0   0/2     Pending
   17:27:42 vali-0   0/2     Pending
   17:27:42 vali-0   0/2     Init:0/2
   17:27:42 vali-0   0/2     Init:0/2
   17:27:43 vali-0   0/2     Init:1/2
   17:27:44 vali-0   0/2     PodInitializing
   17:27:45 vali-0   1/2     Running
   17:27:46 vali-0   2/2     Running
   ```
   
   </details>
   
   Co-authored-by: Istvan Zoltan Ballok <istvan.zoltan.ballok@sap.com>
   Co-authored-by: Jeremy Rickards <jeremy.rickards@sap.com>

   

   2 people authored and gardener-ci-robot committed May 25, 2023
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