Fail2Ban Prometheus Exporter

Go tool to collect and export metrics on Fail2Ban

Table of Contents

1. Introduction
2. Running the Exporter
3. Running in Docker
4. Metrics

1. Introduction

The exporter can collect metrics from 2 locations: the fail2ban server socket and the fail2ban server database.

Once the exporter is running, metrics are available at localhost:9191/metrics.

(The default port is 9191 but can be modified with the -port flag)

The exporter communicates with the fail2ban server over its socket. This allows the data collected by the exporter to always align with the output of the fail2ban-client.

The default location of the socket is: /var/run/fail2ban/fail2ban.sock

2. Running the Exporter

The exporter is compiled and released as a single binary. This makes it very easy to run in any environment. No additional runtime dependencies are required.

Compiled binaries for various platforms are provided in each release. See the releases page for more information.

Usage

$ fail2ban-prometheus-exporter -h

  -web.listen-address string
        address to use for metrics server (default 0.0.0.0)
  -port int
        port to use for the metrics server (default 9191)
  -socket string
        path to the fail2ban server socket
  -version
        show version info and exit
  -collector.textfile
        enable the textfile collector
  -collector.textfile.directory string
        directory to read text files with metrics from

Example

fail2ban-prometheus-exporter -socket /var/run/fail2ban/fail2ban.sock -port 9191

Note that the exporter will need read access to the fail2ban socket.

2.1. Compile from Source

The code can be compiled from source by running go build inside the src/ folder. Go version 1.15 or greater is required.

Run go mod download to download all necessary dependencies before running the build.

3. Running in Docker

An official docker image is available on the Gitlab container registry. Use it by pulling the following image:

registry.gitlab.com/hectorjsmith/fail2ban-prometheus-exporter:latest

Use the :latest tag to get the most up to date code (less stable) or use one of the version tagged images to use a specific release. See the registry page for all available tags.

3.1. Volumes

The docker image is designed to run by mounting the fail2ban run folder. The run folder should be mounted in the container at: /var/run/fail2ban.

The folder can be mounted with read-only (ro) permissions.

NOTE: While it is possible to mount the fail2ban.sock file directly, it is recommended to mount the parent folder instead. The .sock file is deleted by fail2ban on shutdown and re-created on startup and this causes problems for the docker mount. See this reply for more details.

3.2. Docker run

Use the following command to run the exporter as a docker container.

docker run -d \
    --name "fail2ban-exporter" \
    -v /var/run/fail2ban:/var/run/fail2ban:ro \
    -p "9191:9191" \
    registry.gitlab.com/hectorjsmith/fail2ban-prometheus-exporter:latest

3.3. Docker compose

The following is a simple docker-compose file to run the exporter.

version: "2"
services:
  exporter:
    image: registry.gitlab.com/hectorjsmith/fail2ban-prometheus-exporter:latest
    volumes:
    - /var/run/fail2ban/:/var/run/fail2ban:ro
    ports:
    - "9191:9191"

4. Metrics

Access exported metrics at the /metrics path on the configured port.

Note on Fail2Ban Jails

fail2ban can be configured to process different log files and use different rules for each one. These separate configurations are referred to as jails.

For example, fail2ban can be configured to watch the system logs for failed SSH connections and Nextcloud logs for failed logins. In this configuration, there will be two jails - one for IPs banned from the SSH logs, and one for IPs banned from the Nextcloud logs.

This tool exports several metrics per jail, meaning that it is possible to track how many IPs are being banned in each jail as well as the overall total. This can be useful to track what services are seeing more failed logins.

4.1. Socket-based Metrics

These are the metrics exported by reading data from the fail2ban server socket. All metrics are prefixed with f2b_.

Exposed metrics:

• up - Returns 1 if the fail2ban server is up and connection succeeds
• errors - Number of errors since startup
  • db - Errors connecting to the database
  • socket_conn - Errors connecting to the fail2ban socket (e.g. connection refused)
  • socket_req - Errors sending requests to the fail2ban server (e.g. invalid responses)
• jail_count - Number of jails configured in fail2ban
• jail_banned_current (per jail) - Number of IPs currently banned
• jail_banned_total (per jail) - Total number of banned IPs since fail2ban startup (includes expired bans)
• jail_failed_current (per jail) - Number of current failures
• jail_failed_total (per jail) - Total number of failures since fail2ban startup
• jail_config_ban_time (per jail) - How long an IP is banned for in this jail (in seconds)
• jail_config_find_time (per jail) - How far back the filter will look for failures in this jail (in seconds)
• jail_config_max_retry (per jail) - The max number of failures allowed before banning an IP in this jail
• version - Version string of the exporter and fail2ban

Sample

# HELP f2b_errors Number of errors found since startup
# TYPE f2b_errors counter
f2b_errors{type="db"} 0
f2b_errors{type="socket_conn"} 0
f2b_errors{type="socket_req"} 0
# HELP f2b_jail_banned_current Number of IPs currently banned in this jail
# TYPE f2b_jail_banned_current gauge
f2b_jail_banned_current{jail="recidive"} 5
f2b_jail_banned_current{jail="sshd"} 15
# HELP f2b_jail_banned_total Total number of IPs banned by this jail (includes expired bans)
# TYPE f2b_jail_banned_total gauge
f2b_jail_banned_total{jail="recidive"} 6
f2b_jail_banned_total{jail="sshd"} 31
# HELP f2b_jail_count Number of defined jails
# TYPE f2b_jail_count gauge
f2b_jail_count 2
# HELP f2b_jail_failed_current Number of current failures on this jail's filter
# TYPE f2b_jail_failed_current gauge
f2b_jail_failed_current{jail="recidive"} 5
f2b_jail_failed_current{jail="sshd"} 6
# HELP f2b_jail_failed_total Number of total failures on this jail's filter
# TYPE f2b_jail_failed_total gauge
f2b_jail_failed_total{jail="recidive"} 7
f2b_jail_failed_total{jail="sshd"} 125
# HELP f2b_config_jail_ban_time How long an IP is banned for in this jail (in seconds)
# TYPE f2b_config_jail_ban_time gauge
f2b_config_jail_ban_time{jail="recidive"} 604800
f2b_config_jail_ban_time{jail="sshd"} 600
# HELP f2b_config_jail_find_time How far back will the filter look for failures in this jail (in seconds)
# TYPE f2b_config_jail_find_time gauge
f2b_config_jail_find_time{jail="recidive"} 86400
f2b_config_jail_find_time{jail="sshd"} 600
# HELP f2b_config_jail_max_retries The number of failures allowed until the IP is banned by this jail
# TYPE f2b_config_jail_max_retries gauge
f2b_config_jail_max_retries{jail="recidive"} 5
f2b_config_jail_max_retries{jail="sshd"} 5
# HELP f2b_up Check if the fail2ban server is up
# TYPE f2b_up gauge
f2b_up 1
# HELP f2b_version Version of the exporter and fail2ban server
# TYPE f2b_version gauge
f2b_version{exporter="0.3.0",fail2ban="0.11.1"} 1

The metrics above correspond to the matching fields in the fail2ban-client status <jail> command:

Status for the jail: sshd|- Filter
|  |- Currently failed: 6
|  |- Total failed:     125
|  `- File list:        /var/log/auth.log
`- Actions
   |- Currently banned: 15
   |- Total banned:     31
   `- Banned IP list:   ...

4.2. Textfile Metrics

For more flexibility the exporter also allows exporting metrics collected from a text file.

To enable textfile metrics:

1. Enable the collector with -collector.textfile=true
2. Provide the directory to read files from with the -collector.textfile.directory flag

Metrics collected from these files will be exposed directly alongside the other metrics without any additional processing. This means that it is the responsibility of the file creator to ensure the format is correct.

By exporting textfile metrics an extra metric is also exported with an error count for each file:

# HELP textfile_error Checks for errors while reading text files
# TYPE textfile_error gauge
textfile_error{path="file.prom"} 0

NOTE: Any file not ending with .prom will be ignored.