Using Thanos as Data Source With Scylla Monitoring Stack

Scylla-Monitoring uses Prometheus for metrics collection, which works out-of-the-box, but Prometheus does have limitations. Thanos  is an opensource solution which when used on top of Prometheus, provides additiuonal functionalities such as:

  • High-availability.

  • Horizontal scaling.

  • Backup.

The benefit is that with Thanos’ flexible design you can use some or all of these features depending on your requirements.

The rest of this document describes how to place Thanos in front of a multiple Prometheus servers and act as a Grafana datasource instead of Prometheus.

Using Thanos As a Prometheus Aggregator

There are a few reasons why you would need multiple Prometheus servers: if the total number of your time series reaches millions you can reach the limit of a single Prometheus server capacity. Sometimes it is also useful to limit the traffic between data centers, so you can have a Prometheus server per DC.

Prometheus Configuration

We will assume you have two Prometheus servers running.

  1. If you are running Prometheus using a container, you should use an external data directory, make sure it is reachable by other containers.

  2. You will need to add the –web.enable-lifecycle flag to your Prometheus command-line option.

Thanos sidecar

The Thanos sidecar is an agent that read from a local Prometheus. Thanos uses a single docker container for different uses, the container would act differently based on the command line it gets. You will need a sidecar for each of your Prometheus servers. A docker command looks like:

docker run -d \
 -v /path/to/prom/dir:/data/prom:z \
 -i --name sidecar thanosio/thanos \
 sidecar \
 --grpc-address= \
 --grpc-grace-period=1s \
 --http-address= \
 --http-grace-period=1s \
 --prometheus.url=http://prometheus-ip:9090 \
 --tsdb.path=/data/prom \
 -p 10912:10912 \
 -p 10911:10911

After you run the sidecar you should be able to reach it from your browser at: http://{ip}:10912

Thanos query

Thanos query is the aggregator, it expose a Prometheus like API and read from multiple thanos stores (in this case the Thanos stores are the sidecars). You run Thanos query together with Scylla . Assuming that you have two sidecars running on IP addresses: ip1 and ip2, Start the container by running:

docker run -d \
 --name thanos -- thanosio/thanos \
   query \ \
   --log.level=debug \
   --grpc-address= \
   --grpc-grace-period=1s \
   --http-address= \
   --http-grace-period=1s \
   --query.replica-label=prometheus \
   --store={ip1}:10911 --store={ip2}:10911

After you run Thanos query, you can connect to its HTTP server, in the above example at http://{ip}:10903

Update Scylla Data source

The last step is to update the Grafana data source to read from the local Thanos instead of from Prometheus. Edit grafana/datasource.yml and replace DB_ADDRESS with {ip}:10903 (The IP address could be of the container as long as it is reachable).

The file you edit is a template file that replaces the file Grafana uses, next time you start.

Restart the Scylla Monitoring Stack it should now use Thanos.