prometheus.h
A lightweight and simple client library for exposing metrics to Prometheus from C applications, contained in a single header file. It handles formatting the metrics and exposing an HTTP endpoint for the Prometheus scraper to pick them up.
To write an exporter, start by creating a prom_metric_set
and initializing
it.
prom_metric_set metrics;
prom_init(&metrics);
Register metrics by creating instances of prom_metric_def
.
prom_metric_def current_time = {"current_time",
"The current system time", PROM_METRIC_TYPE_COUNTER};
prom_register(&metrics, ¤t_time);
Obtain an instance of prom_metric
by passing any number of labels to the
prom_get
function. If a metric with the given combination of labels does not
exist, it will be created. Multiple calls to prom_get
with the same labels
will return the same pointer, but the labels must always be passed in the same
order.
prom_label foo = {"foo", "bar"};
prom_label bing = {"bing", "bong"};
prom_metric *m = prom_get(&metrics, ¤t_time, 2, foo, bing);
You can start the server in a forked process. Then, you can manipulate the
metric values in the main thread and write them out using prom_flush
.
int pid = fork();
if (pid) {
prom_start_server(&metrics, 50950);
} else {
while (1) {
m->value = time(NULL);
prom_flush(&metrics);
sleep(5);
}
}
When you are done, call prom_cleanup
to free the memory used by the metric
set.
prom_cleanup(&metrics);
There are some more practical examples in the examples
directory.
TODO:
- Option to include time in a metric reading
- Handle complex types like summary and histogram