Prometheus Pushgateway

The Prometheus Pushgateway exists to allow ephemeral and batch jobs to expose their metrics to Prometheus. Since these kinds of jobs may not exist long enough to be scraped, they can instead push their metrics to a Pushgateway. The Pushgateway then exposes these metrics to Prometheus.

Non-goals

First of all, the Pushgateway is not capable of turning Prometheus into a push-based monitoring system. For a general description of use cases for the Pushgateway, please read When To Use The Pushgateway.

The Pushgateway is explicitly not an aggregator or distributed counter but rather a metrics cache. It does not have statsd-like semantics. The metrics pushed are exactly the same as you would present for scraping in a permanently running program. If you need distributed counting, you could either use the actual statsd in combination with the Prometheus statsd exporter, or have a look at Weavework's aggregation gateway. With more experience gathered, the Prometheus project might one day be able to provide a native solution, separate from or possibly even as part of the Pushgateway.

For machine-level metrics, the textfile collector of the Node exporter is usually more appropriate. The Pushgateway is intended for service-level metrics.

The Pushgateway is not an event store. While you can use Prometheus as a data source for Grafana annotations, tracking something like release events has to happen with some event-logging framework.

A while ago, we decided to not implement a “timeout” or TTL for pushed metrics because almost all proposed use cases turned out to be anti-patterns we strongly discourage. You can follow a more recent discussion on the prometheus-developers mailing list.

Run it

Download binary releases for your platform from the release page and unpack the tarball.

If you want to compile yourself from the sources, you need a working Go setup. Then use the provided Makefile (type make).

For the most basic setup, just start the binary. To change the address to listen on, use the --web.listen-address flag (e.g. "0.0.0.0:9091" or ":9091"). By default, Pushgateway does not persist metrics. However, the --persistence.file flag allows you to specify a file in which the pushed metrics will be persisted (so that they survive restarts of the Pushgateway).

Using Docker

You can deploy the Pushgateway using the prom/pushgateway Docker image.

For example:

docker pull prom/pushgateway

docker run -d -p 9091:9091 prom/pushgateway

Use it

Configure the Pushgateway as a target to scrape

The Pushgateway has to be configured as a target to scrape by Prometheus, using one of the usual methods. However, you should always set honor_labels: true in the scrape config (see below for a detailed explanation).

Libraries

Prometheus client libraries should have a feature to push the registered metrics to a Pushgateway. Usually, a Prometheus client passively presents metric for scraping by a Prometheus server. A client library that supports pushing has a push function, which needs to be called by the client code. It will then actively push the metrics to a Pushgateway, using the API described below.

Command line

Using the Prometheus text protocol, pushing metrics is so easy that no separate CLI is provided. Simply use a command-line HTTP tool like curl. Your favorite scripting language has most likely some built-in HTTP capabilities you can leverage here as well.

Note that in the text protocol, each line has to end with a line-feed character (aka 'LF' or '\n'). Ending a line in other ways, e.g. with 'CR' aka '\r', 'CRLF' aka '\r\n', or just the end of the packet, will result in a protocol error.

Pushed metrics are managed in groups, identified by a grouping key of any number of labels, of which the first must be the job label. The groups are easy to inspect via the web interface.

For implications of special characters in label values see the URL section below.

Examples:

Push a single sample into the group identified by {job="some_job"}:
```
  echo "some_metric 3.14" | curl --data-binary @- http://pushgateway.example.org:9091/metrics/job/some_job
```
Since no type information has been provided, some_metric will be of type untyped.

Push something more complex into the group identified by {job="some_job",instance="some_instance"}:

  cat <<EOF | curl --data-binary @- http://pushgateway.example.org:9091/metrics/job/some_job/instance/some_instance
  # TYPE some_metric counter
  some_metric{label="val1"} 42
  # TYPE another_metric gauge
  # HELP another_metric Just an example.
  another_metric 2398.283
  EOF

Note how type information and help strings are provided. Those lines are optional, but strongly encouraged for anything more complex.

Delete all metrics in the group identified by {job="some_job",instance="some_instance"}:

  curl -X DELETE http://pushgateway.example.org:9091/metrics/job/some_job/instance/some_instance

Delete all metrics in the group identified by {job="some_job"} (note that this does not include metrics in the {job="some_job",instance="some_instance"} group from the previous example, even if those metrics have the same job label):
```
  curl -X DELETE http://pushgateway.example.org:9091/metrics/job/some_job
```
Delete all metrics in all groups (requires to enable the admin API via the command line flag --web.enable-admin-api):
```
  curl -X PUT http://pushgateway.example.org:9091/api/v1/admin/wipe
```

About the job and instance labels

The Prometheus server will attach a job label and an instance label to each scraped metric. The value of the job label comes from the scrape configuration. When you configure the Pushgateway as a scrape target for your Prometheus server, you will probably pick a job name like pushgateway. The value of the instance label is automatically set to the host and port of the target scraped. Hence, all the metrics scraped from the Pushgateway will have the host and port of the Pushgateway as the instance label and a job label like pushgateway. The conflict with the job and instance labels you might have attached to the metrics pushed to the Pushgateway is solved by renaming those labels to exported_job and exported_instance.

However, this behavior is usually undesired when scraping a Pushgateway. Generally, you would like to retain the job and instance labels of the metrics pushed to the Pushgateway. That's why you have set honor_labels: true in the scrape config for the Pushgateway. It enables the desired behavior. See the documentation for details.

This leaves us with the case where the metrics pushed to the Pushgateway do not feature an instance label. This case is quite common as the pushed metrics are often on a service level and therefore not related to a particular instance. Even with honor_labels: true, the Prometheus server will attach an instance label if no instance label has been set in the first place. Therefore, if a metric is pushed to the Pushgateway without an instance label (and without instance label in the grouping key, see below), the Pushgateway will export it with an empty instance label ({instance=""}), which is equivalent to having no instance label at all but prevents the server from attaching one.

About metric inconsistencies

The Pushgateway exposes all pushed metrics together with its own metrics via the same /metrics endpoint. (See the section about exposed metrics for details.) Therefore, all the metrics have to be consistent with each other: Metrics of the same name must have the same type, even if they are pushed to different groups, and there must be no duplicates, i.e. metrics with the same name and the exact same label pairs. Pushes that would lead to inconsistencies are rejected with status code 400.

Inconsistent help strings are tolerated, though. The Pushgateway will pick a winning help string and log about it at info level.

Legacy note: The help string of Pushgateway's own push_time_seconds metric has changed in v0.10.0. By using a persistence file, metrics pushed to a Pushgateway of an earlier version can make it into a Pushgateway of v0.10.0 or later. In this case, the above mentioned log message will show up. Once each previously pushed group has been deleted or received a new push, the log message will disappear.

The consistency check performed during a push is the same as it happens anyway during a scrape. In common use cases, scrapes happen more often than pushes. Therefore, the performance cost of the push-time check isn't relevant. However, if a large amount of metrics on the Pushgateway is combined with frequent pushes, the push duration might become prohibitively long. In this case, you might consider using the command line flag --push.disable-consistency-check, which saves the cost of the consistency check during a push but allows pushing inconsistent metrics. The check will still happen during a scrape, thereby failing all scrapes for as long as inconsistent metrics are stored on the Pushgateway. Setting the flag therefore puts you at risk to disable the Pushgateway by a single inconsistent push.

About timestamps

If you push metrics at time t₁, you might be tempted to believe that Prometheus will scrape them with that same timestamp t₁. Instead, what Prometheus attaches as a timestamp is the time when it scrapes the Pushgateway. Why so?

In the world view of Prometheus, a metric can be scraped at any time. A metric that cannot be scraped has basically ceased to exist. Prometheus is somewhat tolerant, but if it cannot get any samples for a metric in 5min, it will behave as if that metric does not exist anymore. Preventing that is actually one of the reasons to use a Pushgateway. The Pushgateway will make the metrics of your ephemeral job scrapable at any time. Attaching the time of pushing as a timestamp would defeat that purpose because 5min after the last push, your metric will look as stale to Prometheus as if it could not be scraped at all anymore. (Prometheus knows only one timestamp per sample, there is no way to distinguish a 'time of pushing' and a 'time of scraping'.)

As there aren't any use cases where it would make sense to attach a different timestamp, and many users attempting to incorrectly do so (despite no client library supporting this), the Pushgateway rejects any pushes with timestamps.

If you think you need to push a timestamp, please see When To Use The Pushgateway.

In order to make it easier to alert on failed pushers or those that have not run recently, the Pushgateway will add in the metrics push_time_seconds and push_failure_time_seconds with the Unix timestamp of the last successful and failed POST/PUT to each group. This will override any pushed metric by that name. A value of zero for either metric implies that the group has never seen a successful or failed POST/PUT.

API

All pushes are done via HTTP. The interface is vaguely REST-like.

URL

The default port the Pushgateway is listening to is 9091. The path looks like

/metrics/job/<JOB_NAME>{/<LABEL_NAME>/<LABEL_VALUE>}

<JOB_NAME> is used as the value of the job label, followed by any number of other label pairs (which might or might not include an instance label). The label set defined by the URL path is used as a grouping key. Any of those labels already set in the body of the request (as regular labels, e.g. name{job="foo"} 42) will be overwritten to match the labels defined by the URL path!

If job or any label name is suffixed with @base64, the following job name or label value is interpreted as a base64 encoded string according to RFC 4648, using the URL and filename safe alphabet. (Padding is optional, but a single = is required to encode an empty label value.) This is the only way to handle the following cases:

A job name or a label value that contains a /, because the plain (or even URI-encoded) / would otherwise be interpreted as a path separator.
An empty label value, because the resulting // or trailing / would disappear when the path is sanitized by the HTTP router code. Note that an empty job name is invalid. Empty label values are valid but rarely useful. To encode them with base64, you have to use at least one = padding character to avoid a // or a trailing /.

For other special characters, the usual URI component encoding works, too, but the base64 might be more convenient.

Ideally, client libraries take care of the suffixing and encoding.

Examples:

To use the grouping key job="directory_cleaner",path="/var/tmp", the following path will not work:
```
/metrics/job/directory_cleaner/path//var/tmp
```
Instead, use the base64 URL-safe encoding for the label value and mark it by suffixing the label name with @base64:
```
/metrics/job/directory_cleaner/path@base64/L3Zhci90bXA
```
If you are not using a client library that handles the encoding for you, you can use encoding tools. For example, there is a command line tool base64url (Debian package basez), which you could combine with curl to push from the command line in the following way:
```
echo 'some_metric{foo="bar"} 3.14' | curl --data-binary @- http://pushgateway.example.org:9091/metrics/job/directory_cleaner/path@base64/$(echo -n '/var/tmp' | base64url)
```
To use a grouping key containing an empty label value such as job="example",first_label="",second_label="foobar", the following path will not work:
```
 /metrics/job/example/first_label//second_label/foobar
```
Instead, use the following path including the = padding character:
```
/metrics/job/example/first_label@base64/=/second_label/foobar
```
The grouping key job="titan",name="Προμηθεύς" can be represented “traditionally” with URI encoding:
```
/metrics/job/titan/name/%CE%A0%CF%81%CE%BF%CE%BC%CE%B7%CE%B8%CE%B5%CF%8D%CF%82
```
Or you can use the more compact base64 encoding:
```
/metrics/job/titan/name@base64/zqDPgc6_zrzOt864zrXPjc-C
```

`PUT` method

PUT is used to push a group of metrics. All metrics with the grouping key specified in the URL are replaced by the metrics pushed with PUT.

The body of the request contains the metrics to push either as delimited binary protocol buffers or in the simple flat text format (both in version 0.0.4, see the data exposition format specification). Discrimination between the two variants is done via the Content-Type header. (Use the value application/vnd.google.protobuf; proto=io.prometheus.client.MetricFamily; encoding=delimited for protocol buffers, otherwise the text format is tried as a fall-back.)

The response code upon success is either 200, 202, or 400. A 200 response implies a successful push, either replacing an existing group of metrics or creating a new one. A 400 response can happen if the request is malformed or if the pushed metrics are inconsistent with metrics pushed to other groups or collide with metrics of the Pushgateway itself. An explanation is returned in the body of the response and logged on error level. A 202 can only occur if the --push.disable-consistency-check flag is set. In this case, pushed metrics are just queued and not checked for consistency. Inconsistencies will lead to failed scrapes, however, as described above.

In rare cases, it is possible that the Pushgateway ends up with an inconsistent set of metrics already pushed. In that case, new pushes are also rejected as inconsistent even if the culprit is metrics that were pushed earlier. Delete the offending metrics to get out of that situation.

If using the protobuf format, do not send duplicate MetricFamily proto messages (i.e. more than one with the same name) in one push, as they will overwrite each other.

Note that the Pushgateway doesn't provide any strong guarantees that the pushed metrics are persisted to disk. (A server crash may cause data loss. Or the Pushgateway is configured to not persist to disk at all.)

A PUT request with an empty body effectively deletes all metrics with the specified grouping key. However, in contrast to the DELETE request described below, it does update the push_time_seconds metrics.

`POST` method

POST works exactly like the PUT method but only metrics with the same name as the newly pushed metrics are replaced (among those with the same grouping key).

A POST request with an empty body merely updates the push_time_seconds metrics but does not change any of the previously pushed metrics.

`DELETE` method

DELETE is used to delete metrics from the Pushgateway. The request must not contain any content. All metrics with the grouping key specified in the URL are deleted.

The response code upon success is always 202. The delete request is merely queued at that moment. There is no guarantee that the request will actually be executed or that the result will make it to the persistence layer (e.g. in case of a server crash). However, the order of PUT/POST and DELETE request is guaranteed, i.e. if you have successfully sent a DELETE request and then send a PUT, it is guaranteed that the DELETE will be processed first (and vice versa).

Deleting a grouping key without metrics is a no-op and will not result in an error.

Admin API

The Admin API provides administrative access to the Pushgateway, and must be explicitly enabled by setting --web.enable-admin-api flag.

URL

The default port the Pushgateway is listening to is 9091. The path looks like:

/api/<API_VERSION>/admin/<HANDLER>

Available endpoints:

HTTP_METHOD	API_VERSION	HANDLER	DESCRIPTION
PUT	v1	wipe	Safely deletes all metrics from the Pushgateway.

For example to wipe all metrics from the Pushgateway:

  curl -X PUT http://pushgateway.example.org:9091/api/v1/admin/wipe

Query API

The query API allows accessing pushed metrics and build and runtime information.

URL

/api/<API_VERSION>/<HANDLER>

Available endpoints:

HTTP_METHOD	API_VERSION	HANDLER	DESCRIPTION
GET	v1	status	Returns build information, command line flags, and the start time in JSON format.
GET	v1	metrics	Returns the pushed metric families in JSON format.

For example :

  curl -X GET http://pushgateway.example.org:9091/api/v1/status | jq
  
  {
    "status": "success",
    "data": {
      "build_information": {
        "branch": "master",
        "buildDate": "20200310-20:14:39",
        "buildUser": "flipbyte@localhost.localdomain",
        "goVersion": "go1.13.6",
        "revision": "eba0ec4100873d23666bcf4b8b1d44617d6430c4",
        "version": "1.1.0"
      },
      "flags": {
        "log.format": "logfmt",
        "log.level": "info",
        "persistence.file": "",
        "persistence.interval": "5m0s",
        "push.disable-consistency-check": "false",
        "web.enable-admin-api": "false",
        "web.enable-lifecycle": "false",
        "web.external-url": "",
        "web.listen-address": ":9091",
        "web.route-prefix": "",
        "web.telemetry-path": "/metrics"
      },
      "start_time": "2020-03-11T01:44:49.9189758+05:30"
    }
  }
  
  curl -X GET http://pushgateway.example.org:9091/api/v1/metrics | jq
  
  {
    "status": "success",
    "data": [
      {
        "labels": {
          "job": "batch"
        },
        "last_push_successful": true,
        "my_job_duration_seconds": {
          "time_stamp": "2020-03-11T02:02:27.716605811+05:30",
          "type": "GAUGE",
          "help": "Duration of my batch jon in seconds",
          "metrics": [
            {
              "labels": {
                "instance": "",
                "job": "batch"
              },
              "value": "0.2721322309989773"
            }
          ]
        },
        "push_failure_time_seconds": {
          "time_stamp": "2020-03-11T02:02:27.716605811+05:30",
          "type": "GAUGE",
          "help": "Last Unix time when changing this group in the Pushgateway failed.",
          "metrics": [
            {
              "labels": {
                "instance": "",
                "job": "batch"
              },
              "value": "0"
            }
          ]
        },
        "push_time_seconds": {
          "time_stamp": "2020-03-11T02:02:27.716605811+05:30",
          "type": "GAUGE",
          "help": "Last Unix time when changing this group in the Pushgateway succeeded.",
          "metrics": [
            {
              "labels": {
                "instance": "",
                "job": "batch"
              },
              "value": "1.5838723477166057e+09"
            }
          ]
        }
      }
    ]
  }

Management API

The Pushgateway provides a set of management API to ease automation and integrations.

Available endpoints:

HTTP_METHOD	PATH	DESCRIPTION
GET	/-/healthy	Returns 200 whenever the Pushgateway is healthy.
GET	/-/ready	Returns 200 whenever the Pushgateway is ready to serve traffic.

The following endpoint is disabled by default and can be enabled via the --web.enable-lifecycle flag.

HTTP_METHOD	PATH	DESCRIPTION
PUT	/-/quit	Triggers a graceful shutdown of Pushgateway.

Alternatively, a graceful shutdown can be triggered by sending a SIGTERM to the Pushgateway process.

Exposed metrics

The Pushgateway exposes the following metrics via the configured --web.telemetry-path (default: /metrics):

The pushed metrics.
For each pushed group, a metric push_time_seconds and push_failure_time_seconds as explained above.
The usual metrics provided by the Prometheus Go client library, i.e.:
- process_...
- go_...
- promhttp_metric_handler_requests_...
A number of metrics specific to the Pushgateway, as documented by the example scrape below.

# HELP pushgateway_build_info A metric with a constant '1' value labeled by version, revision, branch, and goversion from which pushgateway was built.
# TYPE pushgateway_build_info gauge
pushgateway_build_info{branch="master",goversion="go1.10.2",revision="8f88ccb0343fc3382f6b93a9d258797dcb15f770",version="0.5.2"} 1
# HELP pushgateway_http_push_duration_seconds HTTP request duration for pushes to the Pushgateway.
# TYPE pushgateway_http_push_duration_seconds summary
pushgateway_http_push_duration_seconds{method="post",quantile="0.1"} 0.000116755
pushgateway_http_push_duration_seconds{method="post",quantile="0.5"} 0.000192608
pushgateway_http_push_duration_seconds{method="post",quantile="0.9"} 0.000327593
pushgateway_http_push_duration_seconds_sum{method="post"} 0.001622878
pushgateway_http_push_duration_seconds_count{method="post"} 8
# HELP pushgateway_http_push_size_bytes HTTP request size for pushes to the Pushgateway.
# TYPE pushgateway_http_push_size_bytes summary
pushgateway_http_push_size_bytes{method="post",quantile="0.1"} 166
pushgateway_http_push_size_bytes{method="post",quantile="0.5"} 182
pushgateway_http_push_size_bytes{method="post",quantile="0.9"} 196
pushgateway_http_push_size_bytes_sum{method="post"} 1450
pushgateway_http_push_size_bytes_count{method="post"} 8
# HELP pushgateway_http_requests_total Total HTTP requests processed by the Pushgateway, excluding scrapes.
# TYPE pushgateway_http_requests_total counter
pushgateway_http_requests_total{code="200",handler="static",method="get"} 5
pushgateway_http_requests_total{code="200",handler="status",method="get"} 8
pushgateway_http_requests_total{code="202",handler="delete",method="delete"} 1
pushgateway_http_requests_total{code="202",handler="push",method="post"} 6
pushgateway_http_requests_total{code="400",handler="push",method="post"} 2

Alerting on failed pushes

It is in general a good idea to alert on push_time_seconds being much farther behind than expected. This will catch both failed pushes as well as pushers being down completely.

To detect failed pushes much earlier, alert on push_failure_time_seconds > push_time_seconds.

Pushes can also fail because they are malformed. In this case, they never reach any metric group and therefore won't set any push_failure_time_seconds metrics. Those pushes are still counted as pushgateway_http_requests_total{code="400",handler="push"}. You can alert on the rate of this metric, but you have to inspect the logs to identify the offending pusher.

Development

The normal binary embeds the web files in the resources directory. For development purposes, it is handy to have a running binary use those files directly (so that you can see the effect of changes immediately). To switch to direct usage, add -tags dev to the flags entry in .promu.yml, and then make build. Switch back to "normal" mode by reverting the changes to .promu.yml and typing make assets.

Contributing

Relevant style guidelines are the Go Code Review Comments and the Formatting and style section of Peter Bourgon's Go: Best Practices for Production Environments.

rock-andy/pushgateway