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chore(docs): update docs for correct use of shell and console and enforce linewidth (#9245)

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# 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](https://cloud.google.com/sql/docs/postgres/high-availability), [AWS](https://docs.aws.amazon.com/prescriptive-guidance/latest/saas-multitenant-managed-postgresql/availability.html),
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.
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.
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.
operate correctly even with few seconds of latency on workspace <-> Coder and
user <-> Coder connections.
## Setup
Coder automatically enters HA mode when multiple instances simultaneously connect
to the same Postgres endpoint.
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](../networking/index.md#custom-relays), Coder ignores `CODER_DERP_SERVER_RELAY_URL` since Postgres is the sole rendezvous for the Coder nodes.
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](../networking/index.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.