From cffabc7a59f566e50edb6c1e13f8045dcad0eebe Mon Sep 17 00:00:00 2001
From: Armin <me@obrown.io>
Date: Fri, 12 May 2017 10:39:08 +0200
Subject: [PATCH] #7083 document logstash.yml ENV interpolation

Fixes #7084
---
 docs/static/settings-file.asciidoc | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/docs/static/settings-file.asciidoc b/docs/static/settings-file.asciidoc
index 622864350..f4c118a96 100644
--- a/docs/static/settings-file.asciidoc
+++ b/docs/static/settings-file.asciidoc
@@ -27,6 +27,24 @@ pipeline.batch.size: 125
 pipeline.batch.delay: 5
 -------------------------------------------------------------------------------------
 
+The `logstash.yml` file also supports bash-style interpolation of environment variables in
+setting values.
+
+[source,yaml]
+-------------------------------------------------------------------------------------
+pipeline:
+  batch:
+    size: ${BATCH_SIZE}
+    delay: ${BATCH_DELAY:5}
+node:
+  name: "node_${LS_NODE_NAME}"
+path:
+   queue: "/tmp/${QUEUE_DIR:queue}"
+-------------------------------------------------------------------------------------
+
+Note that the `${VAR_NAME:default_value}` notation is supported, setting a default batch delay
+of `5` and a default `path.queue` of `/tmp/queue` in the above example.
+
 The `logstash.yml` file includes the following settings:
 
 [options="header"]