Add docs for autodiscover (#5868) (#5879)

* Add docs for autodiscover

* Fix comment on filebeat autodiscover prospector settings

* Apply review comments

* Remove configuration options section

(cherry picked from commit 223c074)

filebeat/docs/autodiscover-docker-config.asciidoc

@@ -0,0 +1,39 @@
+Filebeat supports templates for both prospectors and modules.
+
+["source","yaml",subs="attributes"]
+-------------------------------------------------------------------------------------
+filebeat.autodiscover:
+  providers:
+    - type: docker
+      templates:
+        - condition:
+            equals:
+              docker.container.image: redis
+          config:
+            - type: docker
+              container.ids:
+                - "${data.docker.container.id}"
+              exclude_lines: ["^\\s+[\\-`('.|_]"]  # drop asciiart lines
+-------------------------------------------------------------------------------------
+
+This configuration launches a `docker` logs prospector for all containers running an image with `redis` in the name.
+
+If you are using modules, you can override the default prospector and use the docker prospector instead.
+
+["source","yaml",subs="attributes"]
+-------------------------------------------------------------------------------------
+filebeat.autodiscover:
+  providers:
+    - type: docker
+      templates:
+        - condition:
+            equals:
+              docker.container.image: "redis"
+          config:
+            - module: redis
+              log:
+                prospector:
+                  type: docker
+                  container.ids:
+                    - "${data.docker.container.id}"
+-------------------------------------------------------------------------------------

filebeat/docs/configuring-howto.asciidoc

@@ -36,6 +36,7 @@ The following topics describe how to configure Filebeat:
 * <<configuration-template>>
 * <<configuration-logging>>
 * <<using-environ-vars>>
+* <<configuration-autodiscover>>
 * <<yaml-tips>>
 * <<regexp-support>>
 * <<{beatname_lc}-reference-yml>>
@@ -78,11 +79,12 @@ include::../../libbeat/docs/loggingconfig.asciidoc[]
 :standalone:
 include::../../libbeat/docs/shared-env-vars.asciidoc[]
 
+include::../../libbeat/docs/shared-autodiscover.asciidoc[]
+
 :standalone:
 :allplatforms:
 include::../../libbeat/docs/yaml.asciidoc[]
 
 include::../../libbeat/docs/regexp.asciidoc[]
 
 include::../../libbeat/docs/reference-yml.asciidoc[]
-

libbeat/docs/shared-autodiscover.asciidoc

@@ -0,0 +1,68 @@
+[[configuration-autodiscover]]
+== Autodiscover
+
+Autodiscover allows you to watch for system changes and dynamically adapt settings to them, as they happen.
+This is specially useful when running your infrastructure on containers.
+
+When you run an application on containers it becomes a moving target to the monitoring system. Autodiscover
+allows you to automatically detect what's running and update settings to monitor it.
+
+You can define configuration templates for different containers. Autodiscover subsystem will use them
+to monitor services as they start running.
+
+You define autodiscover settings in the  +{beatname_lc}.autodiscover+ section of the +{beatname_lc}.yml+
+config file. To enable autodiscover, you specify a list of providers.
+
+[float]
+=== Providers
+
+Autodiscover providers work by watching for events on the system and translating those events into internal autodiscover
+events with a common format. When you configure the provider, you can use fields from the autodiscover event to set
+conditions that, when met, launch specific configurations.
+
+[float]
+===== Docker
+
+Docker autodiscover provider watches for Docker containers start and stop. These are the available fields on every
+event:
+
+  * host
+  * port
+  * docker.container.id
+  * docker.container.image
+  * docker.container.name
+  * docker.container.labels
+
+
+For example:
+
+[source,yaml]
+-------------------------------------------------------------------------------------
+{
+  "host": "10.4.15.9",
+  "port": 6379,
+  "docker": {
+    "container": {
+      "id": "382184ecdb385cfd5d1f1a65f78911054c8511ae009635300ac28b4fc357ce51"
+      "name": "redis",
+      "image": "redis:3.2.11",
+      "labels": {
+        "io.kubernetes.pod.namespace": "default"
+        ...
+      }
+    }
+  }
+}
+-------------------------------------------------------------------------------------
+
+You can define a set of configuration templates to be applied when the condition matches an event. Templates define
+a condition to match on autodiscover events, together with the list of configurations to launch when this condition
+happens.
+
+Conditions match events from the provider. Providers use the same format for <<conditions>> that
+processors use.
+
+Configuration templates can contain variables from the autodiscover event. They can be accessed under `data` namespace.
+For example, with the example event, "`${data.port}`" will resolves to `6379`.
+
+include::../../{beatname_lc}/docs/autodiscover-docker-config.asciidoc[]

metricbeat/docs/autodiscover-docker-config.asciidoc

@@ -0,0 +1,18 @@
+Metricbeat supports templates for modules:
+
+["source","yaml",subs="attributes"]
+-------------------------------------------------------------------------------------
+metricbeat.autodiscover:
+  providers:
+    - type: docker
+      templates:
+        - condition:
+            contains:
+              docker.container.image: "redis"
+          config:
+            - module: redis
+              metricsets: ["info", "keyspace"]
+              hosts: "${data.host}:6379"
+-------------------------------------------------------------------------------------
+
+This configuration launches a `redis` module for all containers running an image with `redis` in the name.

metricbeat/docs/configuring-howto.asciidoc

@@ -33,6 +33,7 @@ The following topics describe how to configure Metricbeat:
 * <<configuration-template>>
 * <<configuration-logging>>
 * <<using-environ-vars>>
+* <<configuration-autodiscover>>
 * <<yaml-tips>>
 * <<regexp-support>>
 * <<{beatname_lc}-reference-yml>>
@@ -67,13 +68,12 @@ include::../../libbeat/docs/loggingconfig.asciidoc[]
 :standalone:
 include::../../libbeat/docs/shared-env-vars.asciidoc[]
 
+include::../../libbeat/docs/shared-autodiscover.asciidoc[]
+
 :standalone:
 :allplatforms:
 include::../../libbeat/docs/yaml.asciidoc[]
 
 include::../../libbeat/docs/regexp.asciidoc[]
 
 include::../../libbeat/docs/reference-yml.asciidoc[]
-
-
-