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](https://cloud.google.com/sql/docs/postgres/high-availability),

[AWS](https://docs.aws.amazon.com/prescriptive-guidance/latest/saas-multitenant-managed-postgresql/availability.html),

and other cloud vendors offer fully-managed HA Postgres services that pair

nicely with Coder.

For Coder to operate correctly, Coderd instances should have low-latency

connections to each other so that they can effectively relay traffic between

users and workspaces no matter which Coderd instance users or workspaces connect

to. We make a best-effort attempt to warn the user when inter-Coderd latency is

too high, but if requests start dropping, this is one metric to investigate.

We also recommend that you deploy all Coderd instances such that they have

low-latency connections to Postgres. Coderd often makes several database

round-trips while processing a single API request, so prioritizing low-latency

between Coderd and Postgres is more important than low-latency between users and

Coderd.

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.

Coder automatically enters HA mode when multiple instances simultaneously

connect to the same Postgres endpoint.

HA brings one configuration variable to set in each Coderd 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](./README.md#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:

| Name | `CODER_HTTP_ADDRESS` | `CODER_DERP_SERVER_RELAY_URL` | `CODER_ACCESS_URL` |

| --------- | -------------------- | ----------------------------- | ------------------------ |

| `coder-1` | `*:80` | `http://10.0.0.1:80` | `https://coder.big.corp` |

| `coder-2` | `*:80` | `http://10.0.0.2:80` | `https://coder.big.corp` |

| `coder-3` | `*:80` | `http://10.0.0.3:80` | `https://coder.big.corp` |

If you installed Coder via

[our Helm Chart](../../install/kubernetes.md#4-install-coder-with-helm), 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)

{

"title": "Quotas",

"path": "./admin/users/quotas.md",

"state": "enterprise"

},

{

"title": "High Availability",

"description": "Learn how to configure Coder for High Availability",

"path": "./admin/high-availability.md"

},