# Prometheus Client Library for Modern C++

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This library aims to enable
[Metrics-Driven Development](https://sookocheff.com/post/mdd/mdd/) for
C++ services. It implements the
[Prometheus Data Model](https://prometheus.io/docs/concepts/data_model/),
a powerful abstraction on which to collect and expose metrics. We
offer the possibility for metrics to be collected by Prometheus, but
other push/pull collections can be added as plugins.

## Usage

See https://jupp0r.github.io/prometheus-cpp for more detailed interface documentation.

``` c++
#include <prometheus/counter.h>
#include <prometheus/exposer.h>
#include <prometheus/registry.h>

#include <array>
#include <chrono>
#include <cstdlib>
#include <memory>
#include <string>
#include <thread>

int main() {
  using namespace prometheus;

  // create an http server running on port 8080
  Exposer exposer{"127.0.0.1:8080"};

  // create a metrics registry
  // @note it's the users responsibility to keep the object alive
  auto registry = std::make_shared<Registry>();

  // add a new counter family to the registry (families combine values with the
  // same name, but distinct label dimensions)
  //
  // @note please follow the metric-naming best-practices:
  // https://prometheus.io/docs/practices/naming/
  auto& packet_counter = BuildCounter()
                             .Name("observed_packets_total")
                             .Help("Number of observed packets")
                             .Register(*registry);

  // add and remember dimensional data, incrementing those is very cheap
  auto& tcp_rx_counter =
      packet_counter.Add({{"protocol", "tcp"}, {"direction", "rx"}});
  auto& tcp_tx_counter =
      packet_counter.Add({{"protocol", "tcp"}, {"direction", "tx"}});
  auto& udp_rx_counter =
      packet_counter.Add({{"protocol", "udp"}, {"direction", "rx"}});
  auto& udp_tx_counter =
      packet_counter.Add({{"protocol", "udp"}, {"direction", "tx"}});

  // add a counter whose dimensional data is not known at compile time
  // nevertheless dimensional values should only occur in low cardinality:
  // https://prometheus.io/docs/practices/naming/#labels
  auto& http_requests_counter = BuildCounter()
                                    .Name("http_requests_total")
                                    .Help("Number of HTTP requests")
                                    .Register(*registry);

  // ask the exposer to scrape the registry on incoming HTTP requests
  exposer.RegisterCollectable(registry);

  for (;;) {
    std::this_thread::sleep_for(std::chrono::seconds(1));
    const auto random_value = std::rand();

    if (random_value & 1) tcp_rx_counter.Increment();
    if (random_value & 2) tcp_tx_counter.Increment();
    if (random_value & 4) udp_rx_counter.Increment();
    if (random_value & 8) udp_tx_counter.Increment();

    const std::array<std::string, 4> methods = {"GET", "PUT", "POST", "HEAD"};
    auto method = methods.at(random_value % methods.size());
    // dynamically calling Family<T>.Add() works but is slow and should be
    // avoided
    http_requests_counter.Add({{"method", method}}).Increment();
  }
  return 0;
}

```

## Requirements

Using `prometheus-cpp` requires a C++11 compliant compiler. It has been successfully tested with GNU GCC 7.4 on Ubuntu Bionic (18.04) and Visual Studio 2017.

## Building

There are two supported ways to build
`prometheus-cpp` - [CMake](https://cmake.org)
and [bazel](https://bazel.io). Both are tested in CI and should work
on master and for all releases.

In case these instructions don't work for you, looking at
the [GitHub Workflows](.github/workflows) might help.

### With CMake

For CMake builds don't forget to fetch the submodules first. Please note that
[zlib](https://zlib.net/) and [libcurl](https://curl.se/) are not provided by
the included submodules. In the example below their usage is disabled.

Then build as usual.

``` shell
# fetch third-party dependencies
git submodule init
git submodule update

mkdir _build
cd _build

# run cmake
cmake .. -DBUILD_SHARED_LIBS=ON -DENABLE_PUSH=OFF -DENABLE_COMPRESSION=OFF

# build
cmake --build . --parallel 4

# run tests
ctest -V

# install the libraries and headers
cmake --install .
```

### With Bazel

Install a recent [bazel](https://www.bazel.io) version with Modules support.
To build and test prometheus-cpp run:

```shell
bazel test //...
```

## Packaging

By configuring CPack you can generate an installer like a
Debian package (.deb) or RPM (.rpm) for the static or dynamic
libraries so they can be easily installed on
other systems.

Please refer to the [CPack](https://cmake.org/cmake/help/latest/module/CPack.html)
documentation for all available generators and their
configuration options.

To generate a Debian package you could follow these steps:

``` shell
# fetch third-party dependencies
git submodule update --init

# run cmake
cmake -B_build -DCPACK_GENERATOR=DEB -DBUILD_SHARED_LIBS=ON # or OFF for static libraries

# build and package
cmake --build _build --target package --parallel $(nproc)
```

This will place an appropriately named .deb in the
`_build` folder. To build a RPM package set the `CPACK_GENERATOR`
variable to `RPM`. 

## Consuming the installed project

### CMake

Consuming prometheus-cpp via CMake is the preferred way because all the dependencies
between the three prometheus-cpp libraries are handled correctly.

The `cmake/project-import` directory contains an
example project and minimal [CMakeLists.txt](cmake/project-import-cmake/CMakeLists.txt).

### Ubuntu PPA

The Launchpad [prometheus-cpp team](https://launchpad.net/~prometheus-cpp) provides a
[PPA for stable versions](https://code.launchpad.net/~prometheus-cpp/+archive/ubuntu/prometheus-cpp-stable).
Please follow the "Adding this PPA to your system" steps to use it.

### vcpkg

The [vcpkg](https://github.com/microsoft/vcpkg) package manager contains a
prometheus-cpp port which has been tested on Linux, macOS, and Windows.

### Conan

[Conan](https://conan.io/) package manager contains prometheus-cpp package as well
in [ConanCenter](https://conan.io/center/prometheus-cpp) repository

### Bazel

The Bazel Central Registry (BCR
[provides the prometheus-cpp package](https://registry.bazel.build/modules/prometheus-cpp).
Add the following to your `MODULE.bazel` file:

```python
bazel_dep(name = "prometheus-cpp", version = "1.2.4")
```

### Plain Makefiles

When manually linking prometheus-cpp the library order matters. The needed
libraries depend on the individual use case but the following should work for the pull metrics approach:

```
-lprometheus-cpp-pull -lprometheus-cpp-core -lz
```

For the push-workflow please try:

```
-lprometheus-cpp-push -lprometheus-cpp-core -lcurl -lz
```

## Contributing

Please adhere to the [Google C++ Style
Guide](https://google.github.io/styleguide/cppguide.html). Make sure
to clang-format your patches before opening a PR. Also make sure to
adhere to [these commit message
guidelines](https://chris.beams.io/posts/git-commit/).

You can check out this repo and build the library using
``` bash
bazel build //...
```

Run the unit tests using
```
bazel test //...
```

There is also an integration test that
uses [telegraf](https://github.com/influxdata/telegraf) to scrape a
sample server. With telegraf installed, it can be run using
```
bazel test //pull/tests/integration:scrape-test
```

## Benchmarks

There's a benchmark suite you can run:

```
bazel run -c opt //core/benchmarks

INFO: Analysed target //core/benchmarks:benchmarks (0 packages loaded, 0 targets configured).
INFO: Found 1 target...
Target //core/benchmarks:benchmarks up-to-date:
  bazel-bin/core/benchmarks/benchmarks
INFO: Elapsed time: 0.356s, Critical Path: 0.01s, Remote (0.00% of the time): [queue: 0.00%, setup: 0.00%, process: 0.00%]
INFO: 0 processes.
INFO: Build completed successfully, 1 total action
INFO: Build completed successfully, 1 total action
2018-11-30 15:13:14
Run on (4 X 2200 MHz CPU s)
CPU Caches:
  L1 Data 32K (x2)
  L1 Instruction 32K (x2)
  L2 Unified 262K (x2)
  L3 Unified 4194K (x1)
-----------------------------------------------------------------------------------
Benchmark                                            Time           CPU Iterations
-----------------------------------------------------------------------------------
BM_Counter_Increment                                13 ns         12 ns   55616469
BM_Counter_Collect                                   7 ns          7 ns   99823170
BM_Gauge_Increment                                  12 ns         12 ns   51511873
BM_Gauge_Decrement                                  12 ns         12 ns   56831098
BM_Gauge_SetToCurrentTime                          184 ns        183 ns    3928964
BM_Gauge_Collect                                     6 ns          6 ns  117223478
BM_Histogram_Observe/0                             134 ns        124 ns    5665310
BM_Histogram_Observe/1                             122 ns        120 ns    5937185
BM_Histogram_Observe/8                             137 ns        135 ns    4652863
BM_Histogram_Observe/64                            143 ns        143 ns    4835957
BM_Histogram_Observe/512                           259 ns        257 ns    2334750
BM_Histogram_Observe/4096                         1545 ns       1393 ns     620754
BM_Histogram_Collect/0                             103 ns        102 ns    5654829
BM_Histogram_Collect/1                             100 ns        100 ns    7015153
BM_Histogram_Collect/8                             608 ns        601 ns    1149652
BM_Histogram_Collect/64                           1438 ns       1427 ns     515236
BM_Histogram_Collect/512                          5178 ns       5159 ns     114619
BM_Histogram_Collect/4096                        33527 ns      33280 ns      20785
BM_Registry_CreateFamily                           320 ns        316 ns    2021567
BM_Registry_CreateCounter/0                        128 ns        128 ns    5487140
BM_Registry_CreateCounter/1                       2066 ns       2058 ns     386002
BM_Registry_CreateCounter/8                       7672 ns       7634 ns      91328
BM_Registry_CreateCounter/64                     63270 ns      62761 ns      10780
BM_Registry_CreateCounter/512                   560714 ns     558328 ns       1176
BM_Registry_CreateCounter/4096                18672798 ns   18383000 ns         35
BM_Summary_Observe/0/iterations:262144            9351 ns       9305 ns     262144
BM_Summary_Observe/1/iterations:262144            9242 ns       9169 ns     262144
BM_Summary_Observe/8/iterations:262144           14344 ns      14195 ns     262144
BM_Summary_Observe/64/iterations:262144          19176 ns      18950 ns     262144
BM_Summary_Collect/0/0                              31 ns         30 ns   24873766
BM_Summary_Collect/1/0                             166 ns        166 ns    4266706
BM_Summary_Collect/8/0                            1040 ns       1036 ns     660527
BM_Summary_Collect/64/0                           4529 ns       4489 ns     155600
BM_Summary_Collect/0/1                              28 ns         28 ns   24866697
BM_Summary_Collect/1/1                             190 ns        188 ns    3930354
BM_Summary_Collect/8/1                            1372 ns       1355 ns     535779
BM_Summary_Collect/64/1                           9901 ns       9822 ns      64632
BM_Summary_Collect/0/8                              29 ns         29 ns   24922651
BM_Summary_Collect/1/8                             217 ns        215 ns    3278381
BM_Summary_Collect/8/8                            2275 ns       2256 ns     282503
BM_Summary_Collect/64/8                          56790 ns      55804 ns      13878
BM_Summary_Collect/0/64                             32 ns         31 ns   22548350
BM_Summary_Collect/1/64                            395 ns        389 ns    1817073
BM_Summary_Collect/8/64                          10187 ns      10064 ns      71928
BM_Summary_Collect/64/64                        374835 ns     373560 ns       1812
BM_Summary_Collect/0/512                            28 ns         28 ns   25234228
BM_Summary_Collect/1/512                          1710 ns       1639 ns     802285
BM_Summary_Collect/8/512                         50355 ns      49335 ns      15975
BM_Summary_Collect/64/512                      2520972 ns    2493417 ns        295
BM_Summary_Collect/0/4096                           31 ns         31 ns   24059034
BM_Summary_Collect/1/4096                         2719 ns       2698 ns     286186
BM_Summary_Collect/8/4096                       121689 ns     119995 ns       5647
BM_Summary_Collect/64/4096                     5660131 ns    5587634 ns        134
BM_Summary_Collect/0/32768                          29 ns         29 ns   22217567
BM_Summary_Collect/1/32768                        4344 ns       4294 ns     138135
BM_Summary_Collect/8/32768                      331563 ns     326403 ns       2017
BM_Summary_Collect/64/32768                   16363553 ns   16038182 ns         44
BM_Summary_Collect/0/262144                         27 ns         27 ns   23923036
BM_Summary_Collect/1/262144                      10457 ns      10332 ns      67690
BM_Summary_Collect/8/262144                     930434 ns     869234 ns        792
BM_Summary_Collect/64/262144                  39217069 ns   39054846 ns         13
BM_Summary_Observe_Common/iterations:262144       5587 ns       5557 ns     262144
BM_Summary_Collect_Common/0                        676 ns        673 ns    1054630
BM_Summary_Collect_Common/1                        709 ns        705 ns     990659
BM_Summary_Collect_Common/8                       1030 ns       1025 ns     685649
BM_Summary_Collect_Common/64                      2066 ns       2055 ns     339969
BM_Summary_Collect_Common/512                     5754 ns       5248 ns     156895
BM_Summary_Collect_Common/4096                   23894 ns      23292 ns      31096
BM_Summary_Collect_Common/32768                  49831 ns      49292 ns      13492
BM_Summary_Collect_Common/262144                128723 ns     126987 ns       5579
```

## Project Status
Stable and used in production.

Parts of the library are instrumented by itself
(bytes scraped, number of scrapes, scrape request latencies).  There
is a working [example](pull/tests/integration/sample_server.cc) that's
scraped by telegraf as part of integration tests.

## FAQ

### What scrape formats do you support

Only the [Prometheus Text Exposition
Format](https://github.com/prometheus/docs/blob/master/content/docs/instrumenting/exposition_formats.md#text-format-details).
Support for the protobuf format was removed because it's been removed
from Prometheus 2.0.

## License

MIT
