Add PushGateway docs

Signed-off-by: Fabian Stäber <[email protected]>

Author: fstab

docs/content/config/config.md

@@ -137,3 +137,13 @@ Exporter OpenTelemetry Properties
 (3) Format: `key1=value1,key2=value2`
 
 Many of these attributes can alternatively be configured via OpenTelemetry environment variables, like `OTEL_EXPORTER_OTLP_ENDPOINT`. The Prometheus metrics library has support for OpenTelemetry environment variables. See Javadoc for details.
+
+Exporter PushGateway Properties
+-------------------------------
+
+| Name                                       | Javadoc                                                                                                                                         | Note |
+|--------------------------------------------|-------------------------------------------------------------------------------------------------------------------------------------------------|------|
+| io.prometheus.exporter.pushgateway.address | [PushGateway.Builder.address()](/client_java/api/io/prometheus/metrics/exporter/pushgateway/PushGateway.Builder.html#address(java.lang.String)) | |
+| io.prometheus.exporter.pushgateway.scheme  | [PushGateway.Builder.scheme()](/client_java/api/io/prometheus/metrics/exporter/pushgateway/PushGateway.Builder.html#scheme(java.lang.String))   | |
+| io.prometheus.exporter.pushgateway.job     | [PushGateway.Builder.job()](/client_java/api/io/prometheus/metrics/exporter/pushgateway/PushGateway.Builder.html#job(java.lang.String))         | |
+

docs/content/exporters/pushgateway.md

@@ -0,0 +1,103 @@
+---
+title: Pushgateway
+weight: 5
+---
+
+The [Prometheus Pushgateway](https://github.com/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](/client_java/api/io/prometheus/metrics/exporter/pushgateway/PushGateway.html) Java class allows you to push metrics to a Prometheus Pushgateway.
+
+Example
+-------
+
+{{< tabs "uniqueid" >}}
+{{< tab "Gradle" >}}
+```
+implementation 'io.prometheus:prometheus-metrics-core:1.3.0'
+implementation 'io.prometheus:prometheus-metrics-exporter-pushgateway:1.3.0'
+```
+{{< /tab >}}
+{{< tab "Maven" >}}
+```xml
+<dependency>
+    <groupId>io.prometheus</groupId>
+    <artifactId>prometheus-metrics-core</artifactId>
+    <version>1.3.0</version>
+</dependency>
+<dependency>
+    <groupId>io.prometheus</groupId>
+    <artifactId>prometheus-metrics-exporter-pushgateway</artifactId>
+    <version>1.3.0</version>
+</dependency>
+```
+{{< /tab >}}
+{{< /tabs >}}
+
+```java
+public class ExampleBatchJob {
+
+    private static PushGateway pushGateway = PushGateway.builder()
+            .address("localhost:9091") // not needed as localhost:9091 is the default
+            .job("example")
+            .build();
+
+    private static Gauge dataProcessedInBytes = Gauge.builder()
+            .name("data_processed")
+            .help("data processed in the last batch job run")
+            .unit(Unit.BYTES)
+            .register();
+
+    public static void main(String[] args) throws Exception {
+        try {
+            long bytesProcessed = processData();
+            dataProcessedInBytes.set(bytesProcessed);
+        } finally {
+            pushGateway.push();
+        }
+    }
+
+    public static long processData() {
+        // Imagine a batch job here that processes data
+        // and returns the number of Bytes processed.
+        return 42;
+    }
+}
+```
+
+Basic Auth
+----------
+
+The [PushGateway](/client_java/api/io/prometheus/metrics/exporter/pushgateway/PushGateway.html) supports basic authentication.
+
+```java
+PushGateway pushGateway = PushGateway.builder()
+    .job("example")
+    .basicAuth("my_user", "my_password")
+    .build();
+```
+
+The `PushGatewayTestApp` in `integration-tests/it-pushgateway` has a complete example of this.
+
+SSL
+---
+
+The [PushGateway](/client_java/api/io/prometheus/metrics/exporter/pushgateway/PushGateway.html) supports SSL.
+
+```java
+PushGateway pushGateway = PushGateway.builder()
+    .job("example")
+    .scheme(Scheme.HTTPS)
+    .build();
+```
+
+However, this requires that the JVM can validate the server certificate.
+
+If you want to skip certificate verification, you need to provide your own  [HttpConnectionFactory](/client_java/api/io/prometheus/metrics/exporter/pushgateway/HttpConnectionFactory.html).
+The `PushGatewayTestApp` in `integration-tests/it-pushgateway` has a complete example of this.
+
+Configuration Properties
+------------------------
+
+The [PushGateway](/client_java/api/io/prometheus/metrics/exporter/pushgateway/PushGateway.html) supports a couple of properties that can be configured at runtime. See [config](../../config/config).