Fail2Ban Prometheus Exporter

Collect metrics from a running fail2ban instance.

Table of Contents

1. Quick Start
2. Metrics
3. Configuration
4. Building from source
5. Textfile metrics
6. Troubleshooting

1. Quick Start

The exporter can be run as a standalone binary or a docker container.

1.1. Standalone

The following command will start collecting metrics from the /var/run/fail2ban/fail2ban.sock file and expose them on port 9191.

$ fail2ban_exporter --collector.f2b.socket=/var/run/fail2ban/fail2ban.sock --web.listen-address=":9191"

2022/02/20 09:54:06 fail2ban exporter version 0.8.1
2022/02/20 09:54:06 starting server at :9191
2022/02/20 09:54:06 reading metrics from fail2ban socket: /var/run/fail2ban/fail2ban.sock
2022/02/20 09:54:06 metrics available at '/metrics'
2022/02/20 09:54:06 ready

Binary files for each release can be found on the releases page.

There is also an example systemd service file included in the repository. This is a starting point to run the exporter as a service.

1.2. Docker

Docker run

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

Docker compose

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

Use the :latest tag to get the latest stable release. See the registry page for all available tags.

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.

2. Metrics

The exporter exposes the following metrics:

All metric names are prefixed with f2b_

Metric	Description	Example
up	Returns 1 if the exporter is up and running	f2b_up 1
errors	Count the number of errors since startup by type
errors{type="socket_conn"}	Errors connecting to the fail2ban socket (e.g. connection refused)	f2b_errors{type="socket_conn"} 0
errors{type="socket_req"}	Errors sending requests to the fail2ban server (e.g. invalid responses)	f2b_errors{type="socket_req"} 0
jail_count	Number of jails configured in fail2ban	f2b_jail_count 2
jail_banned_current	Number of IPs currently banned per jail	f2b_jail_banned_current{jail="sshd"} 15
jail_banned_total	Total number of banned IPs since fail2ban startup per jail (includes expired bans)	f2b_jail_banned_total{jail="sshd"} 31
jail_failed_current	Number of current failures per jail	f2b_jail_failed_current{jail="sshd"} 6
jail_failed_total	Total number of failures since fail2ban startup per jail	f2b_jail_failed_total{jail="sshd"} 125
jail_config_ban_time	How long an IP is banned for in this jail (in seconds)	f2b_config_jail_ban_time{jail="sshd"} 600
jail_config_find_time	How far back the filter will look for failures in this jail (in seconds)	f2b_config_jail_find_time{jail="sshd"} 600
jail_config_max_retry	The max number of failures allowed before banning an IP in this jail	f2b_config_jail_max_retries{jail="sshd"} 5
version	Version string of the exporter and fail2ban	f2b_version{exporter="0.5.0",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:   ...

2.1. Grafana

The metrics exported by this tool are compatible with Prometheus and Grafana. A sample grafana dashboard can be found in the grafana.json file. Just import the contents of this file into a new Grafana dashboard to get started.

The dashboard supports displaying data from multiple exporters. Use the instance dashboard variable to select which ones to display.

(Sample dashboard is compatible with Grafana 9.1.8 and above)

3. Configuration

The exporter is configured with CLI flags and environment variables. There are no configuration files.

CLI flags

🚀 Collect prometheus metrics from a running Fail2Ban instance

Flags:
  -h, --help                          Show context-sensitive help.
  -v, --version                       Show version info and exit
      --dry-run                       Attempt to connect to the fail2ban socket then exit
                                      before starting the server
      --web.listen-address=":9191"    Address to use for the metrics server
                                      ($F2B_WEB_LISTEN_ADDRESS)
      --collector.f2b.socket="/var/run/fail2ban/fail2ban.sock"
                                      Path to the fail2ban server socket
                                      ($F2B_COLLECTOR_SOCKET)
      --collector.f2b.exit-on-socket-connection-error
                                      When set to true the exporter will immediately
                                      exit on a fail2ban socket connection error
                                      ($F2B_EXIT_ON_SOCKET_CONN_ERROR)
      --collector.textfile.directory=STRING
                                      Directory to read text files with metrics from
                                      ($F2B_COLLECTOR_TEXT_PATH)
      --web.basic-auth.username=STRING
                                      Username to use to protect endpoints with basic auth
                                      ($F2B_WEB_BASICAUTH_USER)
      --web.basic-auth.password=STRING
                                      Password to use to protect endpoints with basic auth
                                      ($F2B_WEB_BASICAUTH_PASS)

Environment variables

Each environment variable corresponds to a CLI flag. If both are specified, the CLI flag takes precedence.

Environment variable	Corresponding CLI flag
F2B_COLLECTOR_SOCKET	--collector.f2b.socket
F2B_COLLECTOR_TEXT_PATH	--collector.textfile.directory
F2B_WEB_LISTEN_ADDRESS	--web.listen-address
F2B_WEB_BASICAUTH_USER	--web.basic-auth.username
F2B_WEB_BASICAUTH_PASS	--web.basic-auth.password
F2B_EXIT_ON_SOCKET_CONN_ERROR	--collector.f2b.exit-on-socket-connection-error

4. Building from source

Building from source has the following dependencies:

• Go v1.20
• Make

From there, simply run make build

This will download the necessary dependencies and build a fail2ban_exporter binary in the root of the project.

5. Textfile metrics

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

To enable textfile metrics 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.

Running in Docker

To collect textfile metrics inside a docker container, a couple of things need to be done:

1. Mount the folder with the metrics files
2. Set the F2B_COLLECTOR_TEXT_PATH environment variable

For example:

docker run -d \
    --name "fail2ban-exporter" \
    -v /var/run/fail2ban:/var/run/fail2ban:ro \
    -v /path/to/metrics:/app/metrics/:ro \
    -e F2B_COLLECTOR_TEXT_PATH=/app/metrics \
    -p "9191:9191" \
    registry.gitlab.com/hectorjsmith/fail2ban-prometheus-exporter:latest

6. Troubleshooting

6.1. "no such file or directory"

error opening socket: dial unix /var/run/fail2ban/fail2ban.sock: connect: no such file or directory

There are a couple of potential causes for the error above.

File not found

The first is that the file does not exist, so first check that the file path shown in the error actually exists on the system running the exporter. The fail2ban server may be storing the socket file in another location on your machine.

If you are using docker, make sure the correct host folder was mounted to the correct location.

If the file is not in the expected location, you can run the exporter with the corresponding CLI flag or environment variable to use a different file path.

Permissions

If the file does exist, the likely cause are file permissions. By default, the fail2ban server runs as the root user and the socket file can only be accessed by the same user. If you are running the exporter as a non-root user, it will not be able to open the socket file to read/write commands to the server, leading to the error above.

In this case there are a few solutions:

1. Run the exporter as the same user as fail2ban (usually root)
2. Update the fail2ban server config to run as a non-root user, then run the exporter as the same user
3. Update the socket file permissions to be less restrictive

I would recommend option 1. since it is the simplest. Option 2. is a bit more complex, check the fail2ban server documentation for more details. And option 3. is just a temporary fix. The socket file gets re-created each time the fail2ban server is restarted and the original permissions will be restored, so you will need to update the permissions every time the server restarts.