Prometheus Server

One of Promgen’s primary roles is to manage a list of targets for Prometheus to scrape. For high availability, it is generally prefered to have multiple Prometheus servers running together. There are multiple ways to deploy these targets to a Prometheus server.

Worker Model (Push)


Promgen’s Push mode relies on celery to push updates to Prometheus. A Promgen worker is run on each Prometheus server which subscribes to a named queue to signal when to write out an updated configuration file, and update Prometheus.

# Assuming we have a Prometheus shard named promshard and two servers we
# may deploy the workers like this
promgen register-server promshard prometheus001 9090
promgen register-server promshard prometheus002 9090

# Then on each Prometheus server, we would want to run a celery worker with
# the queue name matching the name that we registered
celery -A promgen -l info --queues prometheus001
# If running within docker, the same command would look like this
docker run --rm \
    -v ~/.config/promgen:/etc/promgen/ \
    -v /etc/prometheus:/etc/prometheus \
    line/promgen worker -l info --queues prometheus001

Cron Model (Pull)


In some cases it is not possible (or not desired) to install Promgen beside Prometheus. In this case, Promgne’s pull mode can be used by trigging a small script running from cron or any other job framework. This only requires the server where Prometheus is running, to be able to access Promgen over HTTP.

set -e
# Download all the targets from Promgen to a temporary file
curl http://promgen/api/v1/targets --output /etc/prometheus/targets.tmp
# Optionally you could download from a specific service or project
# curl http://promgen/service/123/targets -o /etc/prometheus/targets.tmp
# curl http://promgen/project/456/targets -o /etc/prometheus/targets.tmp
# Move our file to make it more atomic
mv /etc/prometheus/targets.tmp /etc/prometheus/targets.json
# Tell Prometheus to reload
curl -XPOST http://localhost:9090/-/reload

If it’s possible to install Promgen, then there is a Promgen helper command that handles the same basic steps as the above command. This will however require the Prometheus server to be able to access the same database as the Promgen web instance.

# Internally Promgen uses an atomic write function so you can give
# it the path where you want to save it and have it --reload automatically
promgen targets /etc/prometheus/targets.json --reload

Filtering Targets (Both)

In both models, you will want to ensure that the Prometheus server only scrapes the correct subset of targets. Ensure that the correct rewrite_labels is configured

- job_name: 'promgen'
    - files:
      - "/etc/prometheus/promgen.json"
  - source_labels: [__shard]
    # Our regex value here should match the shard name (exported as __shard)
    # that shows up in Promgen. In the case we want our Prometheus server to
    # scrape all targets, then we can ommit the relable config.
    regex: promshard
    action: keep