Prometheus metrics

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mongoose-os-libs/prometheus-metrics mgos_prometheus_metrics.h    

A Mongoose OS Prometheus Metrics library.


Prometheus is an open-source systems monitoring and alerting toolkit originally built at SoundCloud. Since its inception in 2012, many companies and organizations have adopted Prometheus, and the project has a very active developer and user community. It is now a standalone open source project and maintained independently of any company.

Mongoose OS is a purpose-built secure Operating System for commercial connected devices. It focuses on stable and secure functioning of multiple connected devices in production and post-sale stages. Key features include secure communication (TLS), over-the-air updates (OTA) and remote device management. These features are usually missing from SDK and their correct implementation would be a complex and resource consuming task. Neglecting them may result in compromised device security and negative brand perception of your products.


prometheus-metrics is a library component that can be added to the app's mos.yml file without any configuration needed out of the box, and it pulls in the http-server module. The library opens a /metrics endpoint which exposes the operating system and library vitalsigns to Prometheus.

By adding the library to the build manifest in mos.yml, a compiler define MGOS_HAVE_PROMETHEUS_METRICS is set, which other libraries can use to create metrics and update them. This is non intrusive because if the library is not used, no additional code is compiled in Mongoose OS and its libraries.


Base MGOS Metrics

All Mongoose vitals (memory, WiFi/Ethernet, CPU, scheduling) are exposed using the mgos_ prefix.

# HELP mgos_build Build info
# TYPE mgos_build gauge
mgos_build{app="empty",id="20171121-164823/???",version="1.1.04"} 1
# HELP mgos_platform Platform information
# TYPE mgos_platform gauge
mgos_platform{arch="esp32",mac="240AC4106560",idf="v1.0-2815-g50a73c1"} 1
# HELP mgos_uptime Uptime in seconds
# TYPE mgos_uptime counter
mgos_uptime 1888
# HELP mgos_heap_size System memory size
# TYPE mgos_heap_size gauge
mgos_heap_size 295076

Platform Specific Metrics

Platform specific vitals are exposed using the $platform_ prefix, for example esp32_ for ESP32 and ESP-IDF metrics.

# HELP esp32_chip_info ESP32 Chip Information
# TYPE esp32_chip_info gauge
esp32_chip_info{model=0,cores=2,revision=1,features=32,sdk="master"} 1
# HELP esp32_num_tasks ESP32 FreeRTOS task count
# TYPE esp32_num_tasks gauge
esp32_num_tasks 9

Library Specific Metrics

Library owners gate the code that creates, updates and exposes the metrics by the define MGOS_HAVE_PROMETHEUS_METRICS. Metrics should be defined as static variables to stay private to the implementation. Then, a callback function is installed, and prometheus-metrics will loop over all registered callbacks to allow them to add their metrics to the output.

Taking mqtt as an example:

#include "mgos_prometheus_metrics.h"

static uint32_t metrics_mqtt_sent_topics_count = 0;
static uint32_t metrics_mqtt_sent_topics_bytes_total = 0;
static uint32_t metrics_mqtt_received_topics_count = 0;
static uint32_t metrics_mqtt_received_topics_bytes_total = 0;

static void metrics_mqtt(struct mg_connection *nc, void *user_data) {
  mgos_prometheus_metrics_printf(nc, COUNTER,
    "mgos_mqtt_sent_topics_count", "MQTT topics sent",
    "%u", metrics_mqtt_sent_topics_count);

  mgos_prometheus_metrics_printf(nc, COUNTER,
    "mgos_mqtt_sent_topics_bytes_total", "Total bytes sent in MQTT topics",
    "%u", metrics_mqtt_sent_topics_bytes_total);

  mgos_prometheus_metrics_printf(nc, COUNTER,
    "mgos_mqtt_received_topics_count", "MQTT topics sent",
    "%u", metrics_mqtt_received_topics_count);

  mgos_prometheus_metrics_printf(nc, COUNTER,
    "mgos_mqtt_received_topics_bytes_total", "Total bytes received in MQTT topics",
    "%u", metrics_mqtt_received_topics_bytes_total);

  (void) user_data;

Then in the library's init function, register the callback:

bool mgos_mqtt_init(void) {
  mgos_prometheus_metrics_add_handler(metrics_mqtt, NULL);
  return true;

As mentioned above, if the prometheus-metrics library is not included in the app's mos.yml manifest, no code will be compiled which makes the addition non intrusive.

Application Specific Metrics

Users are able to add their app's own metrics in the same way as libraries can. They do this by registering a handler function, which is called from prometheus-metrics.

#include "mgos_prometheus_metrics.h"
uint32_t my_counter=0;

static void prometheus_metrics_fn(struct mg_connection *nc, void *user_data) {
  mgos_prometheus_metrics_printf(nc, COUNTER,
    "my_counter", "Total things counted",
    "%u", my_counter);
  (void) user_data;

enum mgos_app_init_result mgos_app_init(void) {
  mgos_prometheus_metrics_add_handler(prometheus_metrics_fn, NULL);

POSTing to Pushgateway

Prometheus offers an intermediate receiver called a Pushgateway, see their codebase for details. Some users may not wish to have their Mongoose IoT device listen on the network for HTTP connections to the /metrics endpoint, for security reasons. As an alternative, the library can be configured to close its serving endpoint, and push its metrics upstream instead. In mos.yml:

  - ["prometheus.server_enable", false]
  - ["prometheus.pushgateway", "s", ""]

An example program using a timer to POST every 5 seconds:

#include "mgos.h"
#include "mgos_prometheus_metrics.h"

static void timer_cb(void *user_data) {
  mgos_prometheus_metrics_push("test1", "instance1");
  (void) user_data;

enum mgos_app_init_result mgos_app_init(void) {
  mgos_set_timer(5000, true, timer_cb, NULL);


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void mgos_prometheus_metrics_printf(struct mg_connection *nc,
                                    enum mgos_prometheus_metrics_type_t type,
                                    const char *name, const char *descr,
                                    const char *fmt, ...);

Output a formatted metric tuple to the network connection. For example:

uint32_t my_counter=1234;
mgos_prometheus_metrics_printf(nc, COUNTER, "number_of_requests", "My
                               "%u", my_counter);

will output:

# TYPE number_of_requests counter
# HELP number_of_requests My Description
number_of_requests 1234


typedef void (*mgos_prometheus_metrics_fn_t)(struct mg_connection *nc,
                                             void *user_data);

Prototype of a function which is to be called on each prometheus pull/push.


void mgos_prometheus_metrics_add_handler(mgos_prometheus_metrics_fn_t handler,
                                         void *user_data);

Registers a function handler, which will be called each time Prometheus scrapes our HTTP /metrics endpoint. Libraries and application code can register any number of handlers, which will be called one after another. Example:

#include "mgos_prometheus_metrics.h"
uint32_t my_counter=0;

static void prometheus_metrics_fn(struct mg_connection *nc, void *user_data)
  mgos_prometheus_metrics_printf(nc, COUNTER,
    "my_counter", "Total things counted",
    "%u", my_counter);
  (void) user_data;

enum mgos_app_init_result mgos_app_init(void) {
  mgos_prometheus_metrics_add_handler(prometheus_metrics_fn, NULL);


void mgos_prometheus_metrics_push(const char *job, const char *instance);

Perform an HTTP POST request against the Prometheus Pushgateway specified in the flag prometheus.pushgateway in mos.yml, using 'job' and 'instance'. The job argument is mandatory, but instance can be passed NULL.

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