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Ansible Role: Prometheus Target

An Ansible role for deploying Prometheus targets right from your playbooks.

Installation

via galaxy:

ansible-galaxy install kliwniloc.prometheus_target

# requirements.yml
- src: kliwniloc.prometheus_target

via git:

ansible-galaxy install git+https://github.com/kliwniloc/ansible-role-prometheus-target.git,master

# requirements.yml
- src: https://github.com/kliwniloc/ansible-role-prometheus-target
  name: kliwniloc.prometheus_target

Role Variables

For more details see defaults/main.yml

You need to specify your Prometheus server. The server needs to be present under that that name in your inventory.

prometheus_target_host: "" # Required

You should configure defaults for the exporters you are commonly using. You can configure this in the prometheus_target_exporter_defaults variable. For example if you're using a single target file for node exporters you may add the path to that file as a default for the node exporter. This helps keep the prometheus_target_exporter variable clean.

Anything configured in the prometheus_target_exporter takes precedence over the defaults.

prometheus_target_exporter_defaults: {}
  # node_exporter:
  #   path: /opt/prometheus/targets.yml
  #   host: '{{ inventory_hostname }}:9100'
  # blackbox_exporter:
  #   path: /opt/targets/blackbox.yml
  #   host: 'https://{{ hostvars[inventory_hostname].ansible_host }}'
  #   path_prefix: ''

prometheus_target_exporter: []

You can also add exporter that you want to have deployed without needing to specify them in the prometheus_target_exporter variable by adding them to the prometheus_target_default_exporters variable.

prometheus_target_default_exporters: []
prometheus_target_skip_default_exporters: false

As you usually have most target files in one directory you can specify a target prefix for your target files:

prometheus_target_exporter_target_prefix: ''

This way you only need to pass target.yml instead of /path/to/target.yml as your exporter path. You can additionally define this at the prometheus_target_exporter_defaults and the prometheus_target_exporter level using the path_prefix variable:

prometheus_target_exporter_defaults:
  blackbox_exporter:
    path: /opt/targets/blackbox.yml
    host: 'https://{{ hostvars[inventory_hostname].ansible_host }}'
    path_prefix: '' # Disables configured prefix

This role offers a few strategies that you can use to deploy your targets. The strategy decides how exactly targets are added to the targets file and more importantly how to handle existing configuration.

  • lineinfile is the default strategy and simply appends a line to the target file if it isn't already there.
  • yaml parses the yaml target file and adds the host to it. This might mess with the readability of your yaml file, and you should avoid it if you edit the yaml file manually as well.
  • json parses the json target file and adds the host to it.
prometheus_target_strategy: lineinfile

lineinfile simply uses the Ansible lineinfile module to append a line to the specified targets file. This is usually enough to deploy targets and does not change any of the existing lines of the configuration which is nice if you comment your target files.

You can configure a prefix and suffix for applying the target to your target file. The defaults are configured to add a list with 2 (2 space) indentation levels.

prometheus_target_strategy_lineinfile_prefix: '    - '
prometheus_target_strategy_lineinfile_suffix: ''

So the target file should look something like this:

  - labels:
      my: label
    targets:
+     - host:9100

There are a few handlers that are notified if a new target is added. You will want to use those to reload your Prometheus instance after adding modifying targets. If you manage your target files in git you may also wish to commit the changes via a hook.

You can enable or disable the handlers via the prometheus_target_handler_command_enabled/ prometheus_target_handler_shell_enabled variables and configure become behavior via prometheus_target_handler_command_become*/ prometheus_target_handler_shell_become*.

To run the hook per play instead of per hosts, meaning it only runs once, you can set the prometheus_target_handler_command_run_once / prometheus_target_handler_shell_run_once hooks to true.

The prometheus_target_handler_command and prometheus_target_handler_shell variables map the options of their respective Ansible command and shell module.

prometheus_target_handler_command_enabled: false
prometheus_target_handler_command_become: true
# prometheus_target_handler_command_become_method:
# prometheus_target_handler_command_become_user:
prometheus_target_handler_command_run_once: false
prometheus_target_handler_command: {}

prometheus_target_handler_shell_enabled: false
prometheus_target_handler_shell_become: true
# prometheus_target_handler_shell_become_method:
# prometheus_target_handler_shell_become_user:
prometheus_target_handler_shell_run_once: false
prometheus_target_handler_shell: {}

Example Playbooks

Simple example

- name: Deploy node exporter
  hosts: myhost

  vars: # General configuration. Can be set in group_vars
    prometheus_target_host: prometheus
    prometheus_target_exporter_defaults:
      node_exporter:
        path: /opt/prometheus/targets/node.yml
        host: '{{ inventory_hostname }}:9100'

  roles:
    - role: prometheus.node_exporter # deploy node_exporter service
    - role: kliwniloc.prometheus_target # deploy target
      prometheus_target_exporter:
        - id: node_exporter

Using Target prefix

- name: Deploy node exporter with target prefix
  hosts: myhost

  vars: # General configuration. Can be set in group_vars
    prometheus_target_host: prometheus
    prometheus_target_exporter_target_prefix: /opt/prometheus/targets/
    prometheus_target_exporter_defaults:
      node_exporter:
        path: node.yml
        host: '{{ inventory_hostname }}:9100'
      blackbox_exporter: # Another exporter with different prefix
        path: target.yml
        host: '{{ inventory_hostname }}'
        path_prefix: /opt/prefix/

  roles:
    - role: kliwniloc.prometheus_target
      prometheus_target_exporter:
        - id: node_exporter # -> /opt/prometheus/targets/node.yml
        - { id: node_exporter, path: /target.yml, path_prefix: '' } # -> /target.yml
        - { id: blackbox_exporter, path: blackbox.yml } # -> /opt/prefix/blackbox.yml

Using Handlers

- name: Deploy node exporter and reload Prometheus Docker container
  hosts: myhost

  vars: # General configuration. Can be set in group_vars
    prometheus_target_host: prometheus
    prometheus_target_exporter_defaults:
      node_exporter:
        path: /opt/prometheus/targets/node.yml
        host: '{{ inventory_hostname }}:9100'
    prometheus_target_handler_command_enabled: true
    prometheus_target_handler_command_cmd: docker kill -s SIGHUP prometheus

  roles:
    - role: prometheus.node_exporter # deploy node_exporter service
    - role: kliwniloc.prometheus_target # deploy target
      prometheus_target_exporter: [{ id: node_exporter }]

Multiple exporters

- name: Deploy monitoring
  hosts: mycluster

  vars: # General configuration. Can be set in group_vars
    prometheus_target_host: prometheus
    prometheus_target_exporter_defaults:
      node_exporter:
        path: /opt/prometheus/targets/node.yml
        host: '{{ inventory_hostname }}:9100'
      blackbox_exporter:
        path: /opt/prometheus/targets/blackbox.yml
        host: 'https://{{ hostvars[inventory_hostname].ansible_host }}'

  roles:
    - role: prometheus.node_exporter # deploy node_exporter service
    - role: some_application # deploy web app for blackbox exporter
    - role: kliwniloc.prometheus_target # deploy targets
      prometheus_target_exporter:
        - id: node_exporter # deploy node_exporter with default host
        # deploy an exporter that is not specified in prometheus_target_exporter_defaults
        - { host: exporter_without_id, path: /opt/simple_target4.yml }
        # deploy blackbox_exporter with multiple hosts
        - { id: blackbox_exporter, host: node1.example.org }
        - { id: blackbox_exporter, host: node2.example.org }
        - { id: blackbox_exporter, host: node3.example.org }

Target file matching based on group vars

# Inventory file
[agents_s]
agent-s-[1:2]

[agents_m]
agent-m-[1:2]

[agents:children]
agents_s
agents_m

# group_vars/agents_s.yml
prometheus_target_exporter_defaults:
    node_exporter:
    path: /opt/prometheus/targets/agent_s.yml
    host: '{{ inventory_hostname }}:9100'

# group_vars/agents_m.yml
prometheus_target_exporter_defaults:
    node_exporter:
    path: /opt/prometheus/targets/agent_m.yml
    host: '{{ inventory_hostname }}:9100'

- name: Deploy monitoring
  hosts: agents

  vars:
    prometheus_target_host: prometheus

  roles:
    - role: prometheus.node_exporter # deploy node_exporter service
    - role: kliwniloc.prometheus_target
      prometheus_target_exporter:
        - id: node_exporter

# /opt/prometheus/targets/agent_s.yml
+    - agent-s-1:9100
+    - agent-s-2:9100

# /opt/prometheus/targets/agent_m.yml
+    - agent-m-1:9100
+    - agent-m-2:9100

Troubleshooting

  • Running into locks using handlers

By default, the handler runs for every host that is changed. This can cause issues with locking mechanisms when two hooks run simultaneously. A common example of this is when trying to commit the changes to a repository on the Prometheus host like this:

yaml prometheus_target_handler_shell_enabled: true prometheus_target_handler_shell: chdir: /opt/monitoring cmd: | git add prometheus/targets git commit -m "[ANSIBLE] Add target" git push

When deploying targets on multiple hosts you might get an error like this:

txt fatal: [application -> prometheus]: FAILED! => {"changed": true, "cmd": "git add prometheus/targets\ngit commit -m \"[ANSIBLE] Add target\"\ngit push\n", "delta": "0:00:00.159961", "end": "2023-10-04 17:14:22.711445", "msg": "non-zero return code", "rc": 1, "start": "2023-10-04 17:14:22.551484", "stderr": "remote: error: cannot lock ref 'refs/heads/master': is at 8b37e6aead861cf15a8726b3cfb48ae6dd9d98e6 but expected b372bb8bac22770f241c41efdc9e7a3581060053 \nTo ssh://git_repository\n ! [remote rejected] master -> master (failed to update ref)\nerror: failed to push some refs to 'ssh://git_repository'", "stderr_lines": ["remote: error: cannot lock ref 'refs/heads/master': is at 8b37e6aead861cf15a8726b3cfb48ae6dd9d98e6 but expected b372bb8bac22770f241c41efdc9e7a3581060053 ", "To ssh://git_repository", " ! [remote rejected] master -> master (failed to update ref)", "error: failed to push some refs to 'ssh://git_repository'"], "stdout": "[master 8b37e6a] [ANSIBLE] Add target\n 1 file changed, 3 insertions", "stdout_lines": ["[master 8b37e6a] [ANSIBLE] Add target", " 1 file changed, 3 insertions"]}

To fix this issue you can use the run_once options on the handler like this:

yaml prometheus_target_handler_shell_enabled: true prometheus_target_handler_shell_run_once: true prometheus_target_handler_shell: chdir: /opt/monitoring cmd: | git add prometheus/targets git commit -m "[ANSIBLE] Add target" git push

  • Running into the OpenSSH Max Open Connections limit:

SSH Servers often limit the maximum amount of sessions that may be active / may be currently activating. When deploying the Prometheus target to a large amount of hosts (with many Ansible forks like -f 100), the role will make an SSH connection to the Prometheus server for each host, and you can get an error like this:

txt failed: [application -> prometheus] (item={'id': 'agent'}) => {"ansible_loop_var": "item", "item": {"id": "agent"}, "msg": "Data could not be sent to remote host \"prometheus\". Make sure this host can be reached over ssh: mux_client_request_session: session request failed: Session open refused by peer\r\nkex_exchange_identification: read: Connection reset by peer\r\nConnection reset by 0.0.0.0 port 22\r\n", "unreachable": true} fatal: [application -> {{ prometheus_target_host }}]: UNREACHABLE! => {"changed": false, "msg": "All items completed", "results": [{"ansible_loop_var": "item", "item": {"id": "agent"}, "msg": "Data could not be sent to remote host \"prometheus\". Make sure this host can be reached over ssh: mux_client_request_session: session request failed: Session open refused by peer\r\nkex_exchange_identification: read: Connection reset by peer\r\nConnection reset by 0.0.0.0 port 22\r\n", "unreachable": true}]}

A quick workaround is to just limit the forks of your ansible-playbook command to something that won't overload your server like this: ansible-playbook -f 1 playbook.yml.

To permanently fix the issue you can increase the MaxSession and MaxStartups values in your sshd_config of the Prometheus host.

```man MaxSessions Specifies the maximum number of open shell, login or subsystem (e.g. sftp) sessions permitted per network connection. Multiple sessions may be established by clients that support connection multiplexing. Setting MaxSessions to 1 will effectively disable session multiplexing, whereas setting it to 0 will prevent all shell, login and subsystem sessions while still permitting for- warding. The default is 10.

MaxStartups Specifies the maximum number of concurrent unauthenticated con- nections to the SSH daemon. Additional connections will be dropped until authentication succeeds or the LoginGraceTime expires for a connection. The default is 10:30:100.

  Alternatively, random early drop can be enabled by specifying the
  three colon separated values ``start:rate:full'' (e.g.
  "10:30:60").  sshd(8) will refuse connection attempts with a
  probability of ``rate/100'' (30%) if there are currently
  ``start'' (10) unauthenticated connections.  The probability
  increases linearly and all connection attempts are refused if the
  number of unauthenticated connections reaches ``full'' (60).

```

Dependencies

None.

License

MIT