- Update `synapse_xxx` (server-level) metrics to use
`server_name="$server_name",` instead of `instance="$instance"`
- Add `synapse_server_name_info` metric to map Synapse `server_name`s to
the `instance`s they're hosted on.
- For process level metrics, update to use `xxx * on (instance, job,
index) group_left(server_name)
synapse_server_name_info{server_name="$server_name"}`
All of the changes here are backwards compatible with whatever people
were doing before with their Prometheus/Grafana dashboards.
Previously, the recommendation was to use the `instance` label to group
everything under the same server (803e4b4d88/docs/metrics-howto.md (L93-L147))
But the `instance` label actually has a special meaning and we're
actually abusing it by using it that way:
> `instance`: The `<host>:<port>` part of the target's URL that was
scraped.
>
> *--
https://prometheus.io/docs/concepts/jobs_instances/#automatically-generated-labels-and-time-series*
Since https://github.com/element-hq/synapse/issues/18592 (Synapse
`v1.139.0`), we now have the `server_name` label to use instead.
---
Additionally, the assumption that a single process is serving a single
server is no longer true with [Synapse Pro for small
hosts](https://docs.element.io/latest/element-server-suite-pro/synapse-pro-for-small-hosts/overview/).
Part of https://github.com/element-hq/synapse-small-hosts/issues/106
### Motivating use case
Although this change also benefits [Synapse Pro for small
hosts](https://docs.element.io/latest/element-server-suite-pro/synapse-pro-for-small-hosts/overview/)
(https://github.com/element-hq/synapse-small-hosts/issues/106), this is
actually spawning from adding Prometheus metrics to our workerized
Docker image (https://github.com/element-hq/synapse/pull/19324,
https://github.com/element-hq/synapse/pull/19336) with a more correct
label setup (without `instance`) and wanting the dashboard to be better.
### Testing strategy
1. Make sure your firewall allows the Docker containers to communicate
to the host (`host.docker.internal`) so they can access exposed ports of
other Docker containers. We want to allow Synapse to access the
Prometheus container and Grafana to access to the Prometheus container.
- `sudo ufw allow in on docker0 comment "Allow traffic from the default
Docker network to the host machine (host.docker.internal)"`
- `sudo ufw allow in on br-+ comment "(from Matrix Complement testing)
Allow traffic from custom Docker networks to the host machine
(host.docker.internal)"`
- [Complement firewall
docs](ee6acd9154/README.md (potential-conflict-with-firewall-software))
1. Build the Docker image for Synapse: `docker build -t
matrixdotorg/synapse -f docker/Dockerfile .`
([docs](7a24fafbc3/docker/README-testing.md (building-and-running-the-images-manually)))
1. Generate config for Synapse:
```
docker run -it --rm \
--mount type=volume,src=synapse-data,dst=/data \
-e SYNAPSE_SERVER_NAME=my.docker.synapse.server \
-e SYNAPSE_REPORT_STATS=yes \
-e SYNAPSE_ENABLE_METRICS=1 \
matrixdotorg/synapse:latest generate
```
1. Start Synapse:
```
docker run -d --name synapse \
--mount type=volume,src=synapse-data,dst=/data \
-p 8008:8008 \
-p 19090:19090 \
matrixdotorg/synapse:latest
```
1. You should be able to see metrics from Synapse at
http://localhost:19090/_synapse/metrics
1. Create a Prometheus config (`prometheus.yml`)
```yaml
global:
scrape_interval: 15s
scrape_timeout: 15s
evaluation_interval: 15s
scrape_configs:
- job_name: prometheus
scrape_interval: 15s
metrics_path: /_synapse/metrics
scheme: http
static_configs:
- targets:
# This should point to the Synapse metrics listener (we're using
`host.docker.internal` because this is from within the Prometheus
container)
- host.docker.internal:19090
```
1. Start Prometheus (update the volume bind mount to the config you just
saved somewhere):
```
docker run \
--detach \
--name=prometheus \
--add-host host.docker.internal:host-gateway \
-p 9090:9090 \
-v
~/Documents/code/random/prometheus-config/prometheus.yml:/etc/prometheus/prometheus.yml
\
prom/prometheus
```
1. Make sure you're seeing some data in Prometheus. On
http://localhost:9090/query, search for `synapse_build_info`
1. Start [Grafana](https://hub.docker.com/r/grafana/grafana)
```
docker run -d --name=grafana --add-host
host.docker.internal:host-gateway -p 3000:3000 grafana/grafana
```
1. Visit the Grafana dashboard, http://localhost:3000/ (Credentials:
`admin`/`admin`)
1. **Connections** -> **Data Sources** -> **Add data source** ->
**Prometheus**
- Prometheus server URL: `http://host.docker.internal:9090`
1. Import the Synapse dashboard: `contrib/grafana/synapse.json`
To test workers, you can use the testing strategy from
https://github.com/element-hq/synapse/pull/19336 (assumes both changes
from this PR and the other PR are combined)
It doesn't seem to be documented anywhere and means that you suddenly start losing metrics without any obvious reason when you go from monolith to workers (e.g. #7312).
