Monitoring

Three different jobs, often confused: collecting metrics and alerting on them, catching application errors, and telling users what is broken. Most setups end up with one tool for each.

Metrics and alerting

• Prometheus, Alertmanager and Grafana - Prometheus, Alertmanager and Grafana, pull-based, self-hosted.
• Datadog - SaaS, agent on every host. Container command below.
• New Relic - SaaS, the historical application performance monitoring one.

On Kubernetes these are installed as charts, see Helm.

Error tracking

• Sentry - hosted, and the same product is self-hostable from getsentry/self-hosted (Docker Compose).

Status pages

A status page is what users read when your infrastructure is down, so it is hosted somewhere else than the infrastructure it reports on. That constraint is most of the choice.

• Statuspage - SaaS, the default answer.
• Cachet - self-hosted, PHP.
• Stashboard - Python on App Engine, archived in 2019, do not start here.

Running the Datadog Agent in a container

One agent container per host, with the Docker socket and the host /proc and cgroups mounted read only:

docker run -d --cgroupns host --pid host --name dd-agent \
  -v /var/run/docker.sock:/var/run/docker.sock:ro \
  -v /proc/:/host/proc/:ro \
  -v /sys/fs/cgroup/:/host/sys/fs/cgroup:ro \
  -e DD_SITE=datadoghq.com \
  -e DD_API_KEY=<your api key> \
  registry.datadoghq.com/agent:7

DD_SITE has to match the region your account lives in (it defaults to datadoghq.com); point it at the wrong one and the agent runs happily while nothing shows up in the interface.

What the agent actually sees, checks included:

docker exec -it dd-agent agent status

Both come from the Docker Agent documentation and its Agent commands guide, checked in August 2026.

The image and the variable names changed with Agent 6: datadog/docker-dd-agent was the Agent 5 image, it took API_KEY rather than DD_API_KEY and ran privileged, and its status command was service datadog-agent info. Recipes older than that, mine included, are worth nothing today. The CoreOS unit I used to run it with is kept in CoreOS.