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65 lines
2.8 KiB
Markdown
65 lines
2.8 KiB
Markdown
# High Availability
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High Availability (HA) mode solves for horizontal scalability and automatic failover
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within a single region. When in HA mode, Coder continues using a single Postgres
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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),
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and other cloud vendors offer fully-managed HA Postgres services that pair
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nicely with Coder.
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For Coder to operate correctly, every node must be within 10ms of each other
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and Postgres. We make a best-effort attempt to warn the user when inter-Coder
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latency is too high, but if requests start dropping, this is one metric to investigate.
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Note that this latency requirement applies _only_ to Coder services. Coder will
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operate correctly even with few seconds of latency on
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workspace <-> Coder and user <-> Coder connections.
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## Setup
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> 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.
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Coder automatically enters HA mode when multiple instances simultaneously connect
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to the same Postgres endpoint.
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HA brings one configuration variable to set in each Coder
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node: `CODER_DERP_SERVER_RELAY_URL`. The HA nodes use these URLs to communicate
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with each other. Inter-node communication is only required while using the
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embedded relay (default). If you're using [custom relays](../networking.md#custom-relays), Coder ignores `CODER_DERP_SERVER_RELAY_URL` since Postgres is the sole rendezvous for the Coder nodes.
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`CODER_DERP_SERVER_RELAY_URL` will never be `CODER_ACCESS_URL` because
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`CODER_ACCESS_URL` is a load balancer to all Coder nodes.
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Here's an example 3-node network configuration setup:
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| Name | `CODER_ADDRESS` | `CODER_DERP_SERVER_RELAY_URL` | `CODER_ACCESS_URL` |
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| --------- | --------------- | ----------------------------- | ------------------------ |
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| `coder-1` | `*:80` | `http://10.0.0.1:80` | `https://coder.big.corp` |
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| `coder-2` | `*:80` | `http://10.0.0.2:80` | `https://coder.big.corp` |
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| `coder-3` | `*:80` | `http://10.0.0.3:80` | `https://coder.big.corp` |
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## Kubernetes
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If you installed Coder via
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[our Helm Chart](../install/kubernetes.md#install-coder-with-helm), just
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increase `coder.replicaCount` in `values.yaml`.
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If you installed Coder into Kubernetes by some other means, insert the relay URL
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via the environment like so:
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```yaml
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env:
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- name: POD_IP
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valueFrom:
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fieldRef:
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fieldPath: status.podIP
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- name: CODER_DERP_SERVER_RELAY_URL
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value: http://$(POD_IP)
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```
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Then, increase the number of pods.
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## Up next
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- [Networking](../networking.md)
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- [Kubernetes](../install/kubernetes.md)
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- [Enterprise](../enterprise.md)
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