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Exporter Exporter - prometheus exporter proxy

"you mean apache/nginx" - bbrazil

This provides a simple reverse proxy for prometheus exporters. It is intended as a single binary alternative to nginx/apache for use in environments where opening multiple TCP ports to all servers might be difficult (technically or politically)

The advantages are:

  • A single port can be used to query multiple exporters (to ease firewall configuration concerns).
  • Can provide TLS with optional client certificate authentication.
  • Provides verification that the target is serving prometheus metrics.
  • Can be used to execute scripts that produce prometheus metrics.
  • up behaviour is the same as for querying individual collectors.
  • Small code size, minimal external depedencies, easily auditable.

The exporter has three endpoints.

  • /: displays a list of all exporters with links to their metrics.

    • Returns JSON if the header "Accept: application/json" is passed
  • /proxy: which takes the following parameters:

    • module: the name of the module from the configuration to execute.
    • args: (only for exec modules): additional arguments to the backend command.
    • all other query string parameters are passed on to any http backend module. (excluding the first module parameter value).
  • /metrics: this exposes the metrics for the collector itself.

Features that will NOT be included:

  • merging of module outputs into one query (this would break up behaviour)

Installation

You can build directly using a plain go get github.com/QubitProducts/exporter_exporter. The provided Makefile is primarily used for releases.

Pre-built binaries and a debian package are available on the GitHub release page.

An ansible recipe as also available (kindly provided by one of our users).

TODO:

  • Config reload on HUP (or POST, or config file change?)
  • route to a docker/rocket container by name

Windows Service

The binary can be installed as a Windows service by supplying the -winsvc install arg. All other arguments passed along with -winsvc install will be added to the service startup and can only be changed by uninstalling/installing it again (or modifying the Windows registry directly).

Configuration

In expexp.yaml list each exporter listening on localhost with its known port.

modules:
  node:
    method: http
    http:
       port: 9100

  mtail:
    method: http
    http:
       port: 3903
       headers:
          foo: bar

  cadvisor:
    method: http
    http:
       verify: false
       port: 4194

  netdata:
    method: http
    http:
       port: 19999
       path: '/api/v1/allmetrics?format=prometheus'

  blackbox:
    method: http
    http:
       port: 9115
       path: '/probe'

  somescript:
    method: exec
    timeout: 1s
    exec:
      command: /tmp/myscript.sh
      args:
        - "myarg1"
        - "myarg2"
      env:
        THING: "1"
        THING2: "2"

In your prometheus configuration

scrape_configs:
  - job_name: 'expexp_metrics'
    scrape_interval: 1s
    static_configs:
      - targets: ['host:9999']
  - job_name: 'cadvisor'
    scrape_interval: 5s
    metrics_path: /proxy
    params:
      module:
        - cadvisor
    static_configs:
      - targets: ['host:9999']
  - job_name: 'mtail'
    scrape_interval: 5s
    metrics_path: /proxy
    params:
      module:
        - mtail
    static_configs:
      - targets: ['host:9999']
  - job_name: 'somescript'
    scrape_interval: 5s
    metrics_path: /proxy
    params:
      module:
        - somescript
    static_configs:
      - targets: ['host:9999']
  - job_name: 'blackbox'
    metrics_path: /proxy
    params:
      module:
        - blackbox
        - icmp_example
    static_configs:
      - targets:
        - 8.8.8.8
        - 8.8.4.4
    relabel_configs:
      - source_labels: [__address__]
        target_label: __param_target
      - source_labels: [__param_target]
        target_label: instance
      - target_label: __address__
        replacement: host:9999

Blackbox Exporter

The blackbox exporter also uses the "module" query string parameter. To query it via exporter_exporter we rely on the stripping of the initial "module" parameter. For example

curl http://localhost:9999/proxy\?module\=blackbox\&module\=icmp_example\&target\=8.8.8.8

Will query the icmp_example module in your blackbox configuration.

Directory-based configuration

You can also specify -config.dirs to break the configuration into separate files. The module name is taken from the name of the file (minus the yml/yaml extension), and the configuration for that module goes in at the top level.

Note that if you want to use only this configuration method and not the file-based configuration (-config.file option), you must provide an empty string for the file option : ./exporter_exporter -config.file "" -config.dirs "/etc/exporter_exporter/"

==> expexp.yaml <==
modules: {}

==> expexp.d/node.yaml <==
method: http
http:
   port: 9100

==> expexp.d/mtail.yaml <==
method: http
http:
   port: 3903

TLS configuration

You can use exporter_exporter with TLS to encrypt the traffic, and at the same time enforce strong mutual authentication between the nodes and the prometheus server.

Note that -web.tls.verify will accept any certificate signed by the -web.tls.ca, so you need to create a separate CA for this purpose - or use a self-signed certificate, which acts as its own CA.

Here is a simple configuration example, using one key/cert for the prometheus server and one key/cert shared between all the remote nodes. Firstly, create the keys and certs:

openssl req -x509 -newkey rsa:1024 -keyout prom_node_key.pem -out prom_node_cert.pem -days 29220 -nodes -subj /commonName=prom_node/ -addext "subjectAltName=DNS:prom_node"
openssl req -x509 -newkey rsa:1024 -keyout prometheus_key.pem -out prometheus_cert.pem -days 29220 -nodes -subj /commonName=prometheus/ -addext "subjectAltName=DNS:prometheus"

Create an /etc/prometheus/ssl/ directory on the prometheus server and all the remote nodes. Install both cert.pem files everywhere. It is safe for them to be world-readable.

Install prom_node_key.pem only on the nodes, and set file permissions to protect it so that only exporter_exporter can read it. Similarly, install prometheus_key.pem only on the prometheus server, and set permissions so that only the prometheus process can read it.

Configuration for exporter_exporter on the nodes (here it also disables plain HTTP):

EXPEXP_FLAGS='-web.listen-address= -web.tls.listen-address=:9998
 -web.tls.cert=/etc/prometheus/ssl/prom_node_cert.pem
 -web.tls.key=/etc/prometheus/ssl/prom_node_key.pem
 -web.tls.ca=/etc/prometheus/ssl/prometheus_cert.pem
 -web.tls.verify'

To test, use curl to make a scrape, replacing x.x.x.x with the IP address of the target:

curl --cert /etc/prometheus/ssl/prometheus_cert.pem \
     --key /etc/prometheus/ssl/prometheus_key.pem \
     --cacert /etc/prometheus/ssl/prom_node_cert.pem \
     --resolve prom_node:9998:x.x.x.x \
     -v https://prom_node:9998/proxy?module=node

When this is working, configure your prometheus server to use https. Example:

  - job_name: node
    scrape_interval: 1m
    scrape_timeout: 50s
    file_sd_configs:
      - files:
        - /etc/prometheus/targets.d/node_targets.yml
    scheme: https
    tls_config:
      # Verifying remote identity
      ca_file: /etc/prometheus/ssl/prom_node_cert.pem
      server_name: prom_node
      # Asserting our identity
      cert_file: /etc/prometheus/ssl/prometheus_cert.pem
      key_file: /etc/prometheus/ssl/prometheus_key.pem
    metrics_path: /proxy
    params:
      module: [ node ]
    relabel_configs:
      - source_labels: [__address__]
        target_label: instance
      - source_labels: [__address__]
        regex: '([^:]+)'
        target_label: __address__
        replacement: '${1}:9998'

Example /etc/prometheus/targets.d/node_targets.yml:

- labels: []
  targets:
  - 192.0.2.1
  - 192.0.2.2

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