Troubleshooting and FAQ

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Troubleshooting

helm install failed

Not enough resources

You might see one of these errors from helm install:

Error: failed post-install: timed out waiting for the condition
Error: failed pre-install: timed out waiting for the condition

One of the potential causes is that we couldn't find enough resources to schedule all the services PostHog needs to run. To know if resources are a problem we can check pod status and errors while the helm install command is still running:

  1. check the output for kubectl get pods -n posthog and if you see any pending pods for a long time then that could be the problem
  2. check if the pending pod has scheduling errors using kubectl describe pod <podname> -n posthog. For example, at the end of the events section we could see that we didn't have enough memory to schedule the pod.
Events:
Type Reason Age From Message
---- ------ ---- ---- -------
Normal NotTriggerScaleUp 3m23s cluster-autoscaler pod didn't trigger scale-up:
Warning FailedScheduling 45s (x5 over 3m47s) default-scheduler 0/3 nodes are available: 3 Insufficient memory.

How to fix this: try installing on a bigger Kubernetes cluster.

Connection is not secure

First, check that DNS is set up properly:

nslookup <your-hostname> 1.1.1.1

Note that when using a browser there are various layers of caching and other logic that could make the resolution work (temporarily) even if its not correctly set up.

Kafka crash looping (disk full)

You might see an error similar to this one in the kafka pod

Error while writing to checkpoint file /bitnami/kafka/data/...
java.io.IOException: No space left on device

This tells us that the disk is full. The fastest fix here is to increase the Kafka volume size (this can be done by changing kafka.persistence.size in your values.yaml and running a helm upgrade. Note: you might want to avoid applying other changes if you haven't upgraded recently).

Why did we run into this problem and how to avoid it in the future?

There isn't a way for us to say "if there's less than X% of disk space left, then nuke the oldest data". Instead we have two conditions that restrict, when stuff can be deleted:

  • size (logRetentionBytes: _22_000_000_000) for the minimum size of data on disk before allowed deletion.
  • time (logRetentionHours: 24) for the minimum age before allowed deletion.

We need to configure these well, but monitoring disk util can help catch this problem before we end up in a crash loop.

See more in these stack overflow questions (1, 2, 3).

FAQ

How can I increase storage size?

Change the value (e.g. clickhouse.persistence.size) and run a helm upgrade, which works seamlessly on AWS, GCP and DigitalOcean.

Are the errors I'm seeing important?

Here are some examples of log spam that currently exists in our app and is safe to ignore:

The following messages in the ClickHouse pod happen when ClickHouse reshuffles how it consumes from the topics. So, anytime ClickHouse or Kafka restarts we'll get a bit of noise and the following log entries are safe to ignore:

<Error> TCPHandler: Code: 60, e.displayText() = DB::Exception: Table posthog.sharded_events doesn't exist.
...
<Warning> StorageKafka (kafka_session_recording_events): Can't get assignment. It can be caused by some issue with consumer group (not enough partitions?). Will keep trying.

The following error is produced by some low-priority celery tasks and we haven't seen any actual impact so can safely be ignored. It shows up in Sentry as well.

TooManyConnections: too many connections
File "posthog/celery.py",
...
File "clickhouse_pool/pool.py", line 102, in pull
raise TooManyConnections("too many connections")

How do I see logs for a pod?

  1. Find the name of the pod you want to get logs on:

    kubectl get pods -n posthog

    This command will list all running pods. If you want plugin server logs, for example, look for a pod that has a name starting with posthog-plugins. This will be something like posthog-plugins-54f324b649-66afm

  2. Get the logs for that pod using the name from the previous step:

    kubectl logs posthog-plugins-54f324b649-66afm -n posthog

How do I connect to Postgres?

  1. Find out your Postgres password from the web pod:

    # First we need to determine the name of the web pod – see "How do I see logs for a pod?" for more on this
    POSTHOG_WEB_POD_NAME=$(kubectl get pods -n posthog | grep -- '-web-' | awk '{print $1}')
    # Then we can get the password from the pod's environment variables
    kubectl exec -n posthog -it $POSTHOG_WEB_POD_NAME -- sh -c 'echo The Postgres password is: $POSTHOG_DB_PASSWORD'
  2. Connect to your Postgres pod's shell:

    # We need to determine the name of the Postgres pod (usually it's 'posthog-posthog-postgresql-0')
    POSTHOG_POSTGRES_POD_NAME=$(kubectl get pods -n posthog | grep -- '-postgresql-' | awk '{print $1}')
    # We'll connect straight to the Postgres pod's psql interface
    kubectl exec -n posthog -it $POSTHOG_POSTGRES_POD_NAME -- /bin/bash
  3. Connect to the posthog database:

    You're connecting to your production database, proceed with caution!

    psql -d posthog -U postgres

    Postgres will ask you for the password. Use the value you found out in step 1. Now you can run SQL queries! Just remember that an SQL query needs to be terminated with a semicolon ; to run.

How do I connect to ClickHouse?

Tip: Find out your pod names with kubectl get pods -n posthog

  1. Find out your ClickHouse user and password from the web pod:

    kubectl exec -n posthog -it <your-posthog-web-pod> \
    -- sh -c 'echo user:$CLICKHOUSE_USER password:$CLICKHOUSE_PASSWORD'
  2. Connect to the chi-posthog-posthog-0-0-0 pod:

    kubectl exec -n posthog -it chi-posthog-posthog-0-0-0 -- /bin/bash
  3. Connect to ClickHouse using clickhouse-client:

    Note: You're connecting to your production database, proceed with caution!

    clickhouse-client -d posthog --user <user_from_step_1> --password <password_from_step_1>

How do I restart all pods for a service?

Important: Not all services can be safely restarted this way. It is safe to do this for the plugin server. If you have any doubts, ask someone from the PostHog team.

  1. Terminate all running pods for the service:

    # substitute posthog-plugins for the desired service
    kubectl scale deployment posthog-plugins --replicas=0 -n posthog
  1. Start new pods for the service:

    # substitute posthog-plugins for the desired service
    kubectl scale deployment posthog-plugins --replicas=1 -n posthog

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