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.
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.
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.
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).
You can deploy the Pushgateway using the prom/pushgateway Docker image.
For example:
docker pull prom/pushgateway
docker run -d -p 9091:9091 prom/pushgatewayThe 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).
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.
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.
Caveat: 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.
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_jobSince no type information has been provided,
some_metricwill be of typeuntyped. -
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 EOFNote how type information and help strings are provided. Those lines are optional, but strongly encouraged for anything more complex.
-
Delete all metrics grouped by job and instance:
curl -X DELETE http://pushgateway.example.org:9091/metrics/job/some_job/instance/some_instance -
Delete all metrics grouped by job only:
curl -X DELETE http://pushgateway.example.org:9091/metrics/job/some_job
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 emtpy instance label ({instance=""}),
which is equivalent to having no instance label at all but prevents the
server from attaching one.
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 are essentially no use cases where it would make sense to to attach a different timestamp, and many users attempting to incorrectly do so (despite no client library supporting this) any pushes with timestamps will be rejected.
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 pushers that have not run recently, the
Pushgateway will add in a metric push_time_seconds with the Unix timestamp
of the last POST/PUT to each group. This will override any pushed metric by
that name.
All pushes are done via HTTP. The interface is vaguely REST-like.
The default port the push gateway is listening to is 9091. The path looks like
/metrics/job/<JOBNAME>{/<LABEL_NAME>/<LABEL_VALUE>}
<JOBNAME> 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!
Note that / cannot be used as part of a label value or the job name,
even if escaped as %2F. (The decoding happens before the path
routing kicks in, cf. the Go documentation of
URL.Path.)
There is a deprecated version of the URL path, using jobs instead
of job:
/metrics/jobs/<JOBNAME>[/instances/<INSTANCENAME>]
If this version of the URL path is used with the instances part,
it is equivalent to the URL path above with an instance label, i.e.
/metrics/jobs/foo/instances/bar
is equivalent to
/metrics/job/foo/instance/bar
(Note the missing pluralizations.)
However, if the instances part is missing, the Pushgateway will
automatically use the IP number of the pushing host as the 'instance'
label, and grouping happens by 'job' and 'instance' labels.
Example: Pushing metrics from host 1.2.3.4 using the deprecated URL path
/metrics/jobs/foo
is equivalent to pushing using the URL path
/metrics/job/foo/instance/1.2.3.4
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 always 202 (even if the same grouping key has never been used before, i.e. there is no feedback to the client if the push has replaced an existing group of metrics or created a new one).
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.
A successfully finished request means that the pushed metrics are queued for an update of the storage. Scraping the push gateway may still yield the old results until the queued update is processed. Neither is there a guarantee that the pushed metrics are persisted to disk. (A server crash may cause data loss. Or the push gateway 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 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 is used to delete metrics from the push gateway. 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.
Caution: Up to version 0.1.1 of the Pushgateway, a DELETE request using
the following path (the deprecated form, see above) in the URL would delete
all metrics with the job label 'foo':
/metrics/jobs/foo
Newer versions will treat this path in the same way as
/metrics/job/foo
Note that no implicit addition of an instance label is happening here (in contrast to how the deprecated form of the path is treated during pushing).
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, type DEBUG=1 make assets
just before compiling the binary. Switch back to "normal" mode by
typing make assets.
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.