How to monitor Synapse metrics using Prometheus

1. Install Prometheus:

   Follow instructions at http://prometheus.io/docs/introduction/install/

2. Enable Synapse metrics:

   In homeserver.yaml, make sure enable_metrics is set to True.

3. Enable the /_synapse/metrics Synapse endpoint that Prometheus uses to collect data:

   There are two methods of enabling the metrics endpoint in Synapse.

   The first serves the metrics as a part of the usual web server and can be enabled by adding the "metrics" resource to the existing listener as such:

     resources:
       - names:
         - client
         - metrics
   

   This provides a simple way of adding metrics to your Synapse installation, and serves under /_synapse/metrics. If you do not wish your metrics be publicly exposed, you will need to either filter it out at your load balancer, or use the second method.

   The second method runs the metrics server on a different port, in a different thread to Synapse. This can make it more resilient to heavy load meaning metrics cannot be retrieved, and can be exposed to just internal networks easier. The served metrics are available over HTTP only, and will be available at /_synapse/metrics.

   Add a new listener to homeserver.yaml:

     listeners:
       - type: metrics
         port: 9000
         bind_addresses:
           - '0.0.0.0'
   

4. Restart Synapse.

5. Add a Prometheus target for Synapse.

   It needs to set the metrics_path to a non-default value (under scrape_configs):

     - job_name: "synapse"
       scrape_interval: 15s
       metrics_path: "/_synapse/metrics"
       static_configs:
         - targets: ["my.server.here:port"]
   

   where my.server.here is the IP address of Synapse, and port is the listener port configured with the metrics resource.

   If your prometheus is older than 1.5.2, you will need to replace static_configs in the above with target_groups.

6. Restart Prometheus.

7. Consider using the grafana dashboard and required recording rules

Monitoring workers

To monitor a Synapse installation using workers, every worker needs to be monitored independently, in addition to the main homeserver process. This is because workers don't send their metrics to the main homeserver process, but expose them directly (if they are configured to do so).

To allow collecting metrics from a worker, you need to add a metrics listener to its configuration, by adding the following under worker_listeners:

  - type: metrics
    bind_address: ''
    port: 9101

The bind_address and port parameters should be set so that the resulting listener can be reached by prometheus, and they don't clash with an existing worker. With this example, the worker's metrics would then be available on http://127.0.0.1:9101.

Example Prometheus target for Synapse with workers:

  - job_name: "synapse"
    scrape_interval: 15s
    metrics_path: "/_synapse/metrics"
    static_configs:
      - targets: ["my.server.here:port"]
        labels:
          instance: "my.server"
          job: "master"
          index: 1
      - targets: ["my.workerserver.here:port"]
        labels:
          instance: "my.server"
          job: "generic_worker"
          index: 1
      - targets: ["my.workerserver.here:port"]
        labels:
          instance: "my.server"
          job: "generic_worker"
          index: 2
      - targets: ["my.workerserver.here:port"]
        labels:
          instance: "my.server"
          job: "media_repository"
          index: 1

Labels (instance, job, index) can be defined as anything. The labels are used to group graphs in grafana.

Renaming of metrics & deprecation of old names in 1.2

Synapse 1.2 updates the Prometheus metrics to match the naming convention of the upstream prometheus_client. The old names are considered deprecated and will be removed in a future version of Synapse. The old names will be disabled by default in Synapse v1.71.0 and removed altogether in Synapse v1.73.0.

Removal of deprecated metrics & time based counters becoming histograms in 0.31.0

The duplicated metrics deprecated in Synapse 0.27.0 have been removed.

All time duration-based metrics have been changed to be seconds. This affects:

Several metrics have been changed to be histograms, which sort entries into buckets and allow better analysis. The following metrics are now histograms:

Block and response metrics renamed for 0.27.0

Synapse 0.27.0 begins the process of rationalising the duplicate *:count metrics reported for the resource tracking for code blocks and HTTP requests.

At the same time, the corresponding *:total metrics are being renamed, as the :total suffix no longer makes sense in the absence of a corresponding :count metric.

To enable a graceful migration path, this release just adds new names for the metrics being renamed. A future release will remove the old ones.

The following table shows the new metrics, and the old metrics which they are replacing.

Standard Metric Names

As of synapse version 0.18.2, the format of the process-wide metrics has been changed to fit prometheus standard naming conventions. Additionally the units have been changed to seconds, from milliseconds.

The python-specific counts of garbage collector performance have been renamed.

The twisted-specific reactor metrics have been renamed.