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Updated maps documentation a bit and added first bit of documentation for upstreams.

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Hans van Zijst 2024-12-23 19:35:03 +01:00
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61
matrix/nginx/workers/README.md
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@ -5,10 +5,10 @@ include_toc: true
# Reverse proxy for Synapse with workers # Reverse proxy for Synapse with workers
Changing nginx's configuration from a reverse proxy for a normal, monolithi Changing nginx's configuration from a reverse proxy for a normal, monolithic
Synapse to one for a Synapse that uses workers, quite a lot has to be changed. Synapse to one for a Synapse that uses workers, quite a lot has to be changed.
As mentioned in [Synapse with workers](../synapse/workers.md#synapse), we're As mentioned in [Synapse with workers](../../synapse/workers.md#synapse), we're
changing from network sockets to UNIX sockets. changing from network sockets to UNIX sockets.
Because we're going to have to forward a lot of specific requests to all kinds Because we're going to have to forward a lot of specific requests to all kinds
@ -28,27 +28,24 @@ need to include them several times in different places.
# Maps # Maps
A map sets a variable based on, usually, another variable. One case we use is A map sets a variable based on, usually, another variable. One case we use this
determining the type of sync a client is doing. A normal sync, simply is in determining the type of sync a client is doing. A normal sync, simply
updating an existing session, is a rather lightweight operation. updating an existing session, is a rather lightweight operation. An initial sync,
meaning a full sync because the session is brand new, is not so lightweight.
An initial sync, meaning a full sync because the session is brand new, is not
so lightweight.
A normal sync can be recognised by the `since` bit in the request: it tells A normal sync can be recognised by the `since` bit in the request: it tells
the server when its last sync was. If there is no `since`, we're dealing with the server when its last sync was. If there is no `since`, we're dealing with
an initial sync. an initial sync.
Initial syncs are forwarded to the `initial_sync` workers, the normal syncs to We want to forward requests for normal syncs to the `normal_sync` workers, and
`normal_sync`. the initial syncs to the `initial_sync` workers.
We decide to which type of worker to forward the sync request to by looking at We decide to which type of worker to forward the sync request to by looking at
the presence or absence of `since`: if it's there, it's a normal sync and we the presence or absence of `since`: if it's there, it's a normal sync and we
set the variable `$sync` to `normal_sync`. If it's not there, we set `$sync` to set the variable `$sync` to `normal_sync`. If it's not there, we set `$sync` to
`initial_sync`. `initial_sync`. The content of `since` is irrelevant for nginx.
The last bit is to foward the request to the upstream `$sync`. This is what This is what the map looks like:
that map looks like:
``` ```
map $arg_since $sync { map $arg_since $sync {
@ -57,17 +54,47 @@ map $arg_since $sync {
} }
``` ```
We filter the argument `since` by using `$arg_since`, see [the index of We evaluate `$arg_since` to set `$sync`: `$arg_since` is nginx's variable `$arg_`
followed by `since`, the argument we want. See [the index of
variables in nginx](https://nginx.org/en/docs/varindex.html) for more variables in nginx](https://nginx.org/en/docs/varindex.html) for more
variables we can use. variables we can use in nginx.
By default we set `$sync` to `normal_sync`, unless the argument `since` is By default we set `$sync` to `normal_sync`, unless the argument `since` is
empty (absent); then we set `$sync` to `initial_sync`. empty (absent); then we set it to `initial_sync`.
After that, we forward the request: After this mapping, we forward the request to the correct worker like this:
``` ```
proxy_pass http://$sync; proxy_pass http://$sync;
``` ```
# Upstreams
In our configuration, nginx is not only a reverse proxy, it's a load balancer.
Just like what `haproxy` does, it can forward requests to "servers" behind it.
Such a server is the inbound UNIX socket of a worker, and there can be several
of them in one group.
Two of these upstreams are the sync workers: `normal_sync` and `initial_sync`,
both consisting of several "servers":
```
upstream initial_sync {
hash $mxid_localpart consistent;
server unix:/run/matrix-synapse/inbound_initial_sync1.sock max_fails=0;
server unix:/run/matrix-synapse/inbound_initial_sync2.sock max_fails=0;
keepalive 10;
}
upstream normal_sync {
hash $mxid_localpart consistent;
server unix:/run/matrix-synapse/inbound_normal_sync1.sock max_fails=0;
server unix:/run/matrix-synapse/inbound_normal_sync2.sock max_fails=0;
server unix:/run/matrix-synapse/inbound_normal_sync3.sock max_fails=0;
keepalive 10;
}
```
The `hash` bit is to make sure requests are always forwarded to the same
worker.