prom_rest_exporter

prom_rest_exporter translates arbitrary REST endpoints to metrics for Prometheus.

It uses the excellent jq to transform JSON responses to numeric metric values.

prom_rest_exporter runs as a separate process exposing one or more /metrics endpoints for Prometheus.

Motivation

Sometimes you want to monitor third-party applications that do not provide Prometheus-compatible metrics.
If they provide other REST endpoints with valuable monitoring information, you can use prom_rest_exporter to make these available to Prometheus.

Note: if possible, it’s preferable to adapt the application to provide Prometheus metrics directly. This avoids operational complexity of running prom_rest_exporter in addition to the application.

Installation

Download one of the released binaries.

Run the binary to start prom_rest_exporter.
It expects a configuration file, see below.

Configuration

To configure what REST endpoints should be exported and how,
create a prom_rest_exporter.yml YAML file.

You can also name it differently and use --config <path/to/config.yml> to load it.

Simple config example:

endpoints:
    # Run on localhost:9011/metrics
  - port: 9011
    targets:
        # Get data from this REST endpoint
      - url: https://reqres.in/api/users
        metrics:
          - name: user_count
            description: Number of users
            type: gauge
            # jq program to extract a numeric value from the REST response
            selector: ".total"

See config.md for more detailed information.

Logging

prom_rest_exporter will write log output to prom_rest_exporter.log in the working directory.

Log details can be increased with the --debug and --trace command-line flags.

Error handling

Failures during metric collection, such as REST endpoint downtimes or non-matching metric selectors, are logged but the collection continues for the remaining targets and metrics.

Any metrics that could not be extracted due to errors are simply skipped. Thus, Prometheus will show a “No data” gap when errors occur, and appropriate alerts can be set up for this.

If you enable meta_metrics in your configuration, you will also get the number of skipped
metrics (prom_rest_exp_skipped_metrics) per REST endpoint, and can alert on that.

Development

Dependencies are managed with dep.
Fetch all necessary dependencies with:

dep ensure

jq dependency

Building prom_rest_exporter requires compiled
jq libraries in the vendorc/ folder.

cd vendorc
git clone https://github.com/stedolan/jq.git jq-master
cd jq-master
git checkout jq-1.6
git submodule update --init

Required build tools:

sudo apt-get install autoconf make libtool flex bison gcc-mingw-w64-x86-64

Compiling for linux

autoreconf -fi
./configure --with-oniguruma=builtin --prefix=$PWD/build/linux/usr/local
make -j8
make install
# Remove so files to statically link
rm -f build/linux/usr/local/lib/*.so*

Cross-compiling for Windows

Cf. https://github.com/stedolan/jq/wiki/Cross-compilation

autoreconf -fi
./configure
make distclean
mkdir build
# Run it twice if first time you get "fatal error: compile.h"
CPPFLAGS=-I$PWD/src scripts/crosscompile win64 \
--disable-shared \
--enable-static \
--enable-all-static \
--target=win64-x86_64 \
--host=x86_64-w64-mingw32 \
--with-oniguruma=builtin

Building and testing

Build

go build

Test

go test ./...

Also see .circleci/config.yml for more information on the build process.