Yes. Prometheus can monitor Fail2ban when a Fail2ban-specific exporter reads Fail2ban’s server socket and exposes metrics for Prometheus to scrape. Docker’s built-in Prometheus endpoint reports Docker daemon metrics—not Fail2ban’s state—and seeing a ban metric does not prove that a ban blocks traffic reaching a container.
How the Fail2ban–Prometheus integration works
Fail2ban maintains its state and exposes a server socket. A Fail2ban exporter reads that socket and provides a metrics endpoint; Prometheus scrapes the endpoint. One documented exporter, for example, uses /var/run/fail2ban/fail2ban.sock and exposes metrics on port 9191. Those are that project’s documented defaults, not universal settings: consult the instructions for the exporter you choose. Exporter project documentation
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Mount the socket’s parent directory
The exporter project recommends mounting the directory containing the socket read-only, rather than mounting only the socket file. When Fail2ban stops and starts again, it can remove and recreate the socket; a container mounted to the old file may then have a stale mount. Also check that the exporter process has permission to read the socket.
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Optional textfile metrics
The same project documents an optional textfile collector. Its Docker instructions mount the directory containing the .prom files and configure F2B_COLLECTOR_TEXT_PATH; files without the .prom suffix are ignored. These options are specific to that exporter. Exporter project documentation
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Why Docker daemon metrics are not Fail2ban metrics
Docker can expose Prometheus-compatible metrics for its daemon after you configure metrics-addr. Docker’s example binds the endpoint to 127.0.0.1:9323 and configures a Prometheus container to scrape host.docker.internal:9323. Binding to 0.0.0.0 makes the endpoint available more broadly, so consider the exposure in your network and threat model. Docker: Collect Docker metrics with Prometheus
That endpoint is not an application exporter. Docker’s documentation says, “Currently, you can only monitor Docker itself. You can’t currently monitor your application using the Docker target.” To see Fail2ban state, Prometheus still needs a Fail2ban-specific exporter or another application-level metrics path. Docker also notes that available metrics and their names are actively developed and may change. Docker: Collect Docker metrics with Prometheus
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Choose how Prometheus finds the exporter
Prometheus must be able to reach the exporter’s metrics endpoint on the network where it runs. For a stable, simple deployment, a static scrape target may be sufficient. If containers and their addresses change dynamically, Docker service discovery can identify container addresses, ports, names, images, and labels; relabeling can select or filter the discovered targets. Discovery finds targets, but it does not by itself ensure that Prometheus can connect to them. Prometheus Docker service discovery configuration
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Exporter projects are not interchangeable: ports, flags, supported metrics, and configuration can differ. For example, another project also warns against mounting only the socket file, but that does not make its options identical to the first exporter’s. Compare the chosen project’s current instructions and confirm its socket access and network requirements. go-fail2ban-exporter · mivek/fail2ban-prometheus-exporter
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Monitoring is separate from whether a ban blocks container traffic
A successful scrape shows that Prometheus can read exporter metrics. It does not establish that Fail2ban’s firewall action blocks traffic on the route used to reach a container. Docker documents that traffic to published container ports is routed through NAT before it reaches the INPUT and OUTPUT chains used by ufw, effectively bypassing firewall rules there. Whether a ban works therefore depends on the Fail2ban action, firewall backend, Docker network mode, and published-port path in your setup. Docker: Packet filtering and firewalls
Do not treat disabling Docker’s iptables or nftables management as a routine fix: Docker warns that doing so is likely to break container networking and is not appropriate for most users. Validate the specific traffic path and firewall rules instead. Docker: Packet filtering and firewalls
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Troubleshoot the metrics path and the ban path separately
- Check Fail2ban. Confirm the service is running and that its server socket exists in the host or container where Fail2ban runs.
- Check exporter access. Mount the socket’s parent directory using the selected exporter’s documented mapping, and verify the exporter process can read the socket.
- Check the endpoint. Confirm the exporter starts and that its metrics endpoint is reachable from Prometheus over the actual Docker network or host address.
- Check Prometheus. Inspect the Prometheus Targets page and confirm the exporter target is discovered and its scrape succeeds. Docker’s Prometheus example also uses the Targets page to verify target discovery. Docker: Collect Docker metrics with Prometheus
- Check application metrics. Confirm the expected Fail2ban metrics are present. Docker daemon metrics alone do not report Fail2ban state.
- Test enforcement independently. In a controlled environment, verify that a ban blocks the intended traffic, accounting for the selected Fail2ban action, firewall chain, Docker network mode, and whether the container port is published.
These checks distinguish common failure points: an absent or unreadable socket, an unreachable exporter endpoint, a failed scrape, missing application metrics, or firewall behavior that does not match the container’s traffic path.
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