High Availability

High Availability

High Availability (HA) mode solves for horizontal scalability and automatic failover within a single region. When in HA mode, Coder continues using a single Postgres endpoint. GCP, AWS, and other cloud vendors offer fully-managed HA Postgres services that pair nicely with Coder.

For Coder to operate correctly, every node must be within 10ms of each other and Postgres. We make a best-effort attempt to warn the user when inter-coder latency is too high, but if requests start dropping, this is one metric to investigate. Note that this latency requirement applies only to coder services. Coder will operate correctly even with few seconds of latency on workspace <-> coder and user <-> coder connections.

Setup

We're stress testing High Availability this week before we enable it by default. To try HA beforehand, set CODER_EXPERIMENTAL=true for the Coder server as well as the additional configuration options below.

Coder automatically enters HA mode when multiple instances simultaneously connect to the same Postgres endpoint.

HA brings one configuration variable to set in each Coder node: CODER_DERP_SERVER_RELAY_URL. The HA nodes use these URLs to communicate with each other. Inter-node communication is only required while using the embedded relay (default). If you're using custom relays, Coder ignores CODER_DERP_SERVER_RELAY_URL since Postgres is the sole rendezvous for the Coder nodes.

CODER_DERP_SERVER_RELAY_URL will never be CODER_ACCESS_URL because CODER_ACCESS_URL is a load balancer to all Coder nodes.

Here's an example 3-node network configuration setup:

NameCODER_ADDRESSCODER_DERP_SERVER_RELAY_URLCODER_ACCESS_URL
coder-1*:80http://10.0.0.1:80https://coder.big.corp
coder-2*:80http://10.0.0.2:80https://coder.big.corp
coder-3*:80http://10.0.0.3:80https://coder.big.corp

Kubernetes

If you installed Coder via our Helm Chart, just increase coder.replicaCount in values.yaml.

If you installed Coder into Kubernetes by some other means, insert the relay URL via the environment like so:

env:
  - name: POD_IP
    valueFrom:
      fieldRef:
        fieldPath: status.podIP
  - name: CODER_DERP_SERVER_RELAY_URL
    value: http://$(POD_IP)

Then, increase the number of pods.

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