Add Docker Swarm configuration example (#7542)

Signed-off-by: Julien Pivotto <roidelapluie@inuits.eu>

docs/configuration/configuration.md

@@ -576,6 +576,9 @@ basic_auth:
 [ bearer_token_file: <filename> ]
 ```
 
+See [this example Prometheus configuration file](/documentation/examples/prometheus-dockerswarm.yml)
+for a detailed example of configuring Prometheus for Docker Swarm.
+
 ### `<dns_sd_config>`
 
 A DNS-based service discovery configuration allows specifying a set of DNS

documentation/examples/prometheus-dockerswarm.yml

@@ -0,0 +1,39 @@
+# A example scrape configuration for running Prometheus with
+# Docker Swarm.
+#
+# This example works with cadvisor deployed with:
+# docker service create --name cadvisor -l prometheus-job=cadvisor
+#     --mode=global --publish published=8080,target=8080,mode=host
+#     --mount type=bind,src=/var/run/docker.sock,dst=/var/run/docker.sock,ro
+#     --mount type=bind,src=/,dst=/rootfs,ro
+#     --mount type=bind,src=/var/run,dst=/var/run
+#     --mount type=bind,src=/sys,dst=/sys,ro
+#     --mount type=bind,src=/var/lib/docker,dst=/var/lib/docker,ro
+#     google/cadvisor -docker_only
+
+scrape_configs:
+
+  # Make Prometheus scrape itself for metrics.
+  - job_name: 'prometheus'
+    static_configs:
+    - targets: ['localhost:9090']
+
+  # Create a job for Docker Swarm containers.
+  - job_name: 'dockerswarm'
+    dockerswarm_sd_configs:
+      - host: http://127.0.0.1:2375
+        role: tasks
+    relabel_configs:
+      # Only keep containers that should be running.
+      - source_labels: [__meta_dockerswarm_task_desired_state]
+        regex: running
+        action: keep
+      # Only keep containers that have a `prometheus-job` label.
+      - source_labels: [__meta_dockerswarm_service_label_prometheus_job]
+        regex: .+
+        action: keep
+      # Use the task labels that are prefixed by `prometheus-`.
+      - regex: __meta_dockerswarm_service_label_prometheus_(.+)
+        action: labelmap
+        replacement: $1
+