[imio/helm-plausible-analytics] ClickHouse with multiple replicas and shards

[vittoriocanilli]

I am setting up Plausible with ClickHouse having multiple replicas and shards:

clickhouse:
 auth:
    username: plausible_user
    password: plausible_password
    database: plausible_events_db
  shards: 2
  replicaCount: 3
  resourcesPreset: "medium"
  pdb:
    create: true
    maxUnavailable: 1
  zookeeper:
    enabled: true
    replicaCount: 3
    resourcesPreset: "small"
    pdb:
      create: true
      maxUnavailable: 1

I am using the headless endpoint http://plausible_user:plausible_password@plausible-analytics-clickhouse-headless.<namespace>:8123/plausible_events_db as CLICKHOUSE_DATABASE_URL and everything seems to work.

When I try to delete one of the ClickHouse pods to simulate what would happen during a rescheduling through the Kubernetes cluster's nodes, the pod gets recreated correctly, but the data on the sites on my Plausible dashboard is no more consistent as before: sometimes the graphs have data, sometimes they are empty, sometimes they are not rendered because of a HTTP 500 error.

In this chart's default values I see that you use only one replica and one shard for ClickHouse:

clickhouse:
  shards: 1
  replicaCount: 1

mentioning a Plausible discussion to highlight that Plausible does not support clusters.

I am quite new with ClickHouse: does that actually mean that Plausible can only run with ClickHouse if it has one shard and one replica? Just to understand if it is a limitation of Plausible or of this chart. Thanks in advance.

[alexnuttinck]

Hi @vittoriocanilli,

Indeed, at the time this Helm chart was designed, Plausible did not support ClickHouse in cluster mode, which is why the chart only deploys a single ClickHouse instance with a single replica by default. It’s a regrettable limitation, but it accurately reflects the supported configurations from Plausible when the chart was authored.

If Plausible has since added support for clustered ClickHouse setups, I would be very glad to know! As far as I’m aware, I haven’t seen any official changelogs or documentation indicating that feature has been introduced.

But if anyone has confirmation or details (official docs, examples, or PRs) please share!