[FEAT] Enabled postgres container linking and added a Docker Compose linking example in the README.md.

postgres-backup-s3/README.md

@@ -4,12 +4,38 @@ Backup PostgresSQL to S3 (supports periodic backups)
 
 ## Usage
 
+Docker:
 ```sh
 $ docker run -e S3_ACCESS_KEY_ID=key -e S3_SECRET_ACCESS_KEY=secret -e S3_BUCKET=my-bucket -e S3_PREFIX=backup -e POSTGRES_DATABASE=dbname -e POSTGRES_USER=user -e POSTGRES_PASSWORD=password -e POSTGRES_HOST=localhost schickling/postgres-backup-s3
 ```
 
+Docker Compose:
+```yaml
+postgres:
+  image: postgres
+  environment:
+    POSTGRES_USER: user
+    POSTGRES_PASSWORD: password
+
+pgbackups3:
+  image: schickling/postgres-backup-s3
+  links:
+    - postgres
+  environment:
+    SCHEDULE: '@daily'
+    S3_REGION: region
+    S3_ACCESS_KEY_ID: key
+    S3_SECRET_ACCESS_KEY: secret
+    S3_BUCKET: my-bucket
+    S3_PREFIX: backup
+    POSTGRES_DATABASE: dbname
+    POSTGRES_USER: user
+    POSTGRES_PASSWORD: password
+```
+
 ### Automatic Periodic Backups
 
 You can additionally set the `SCHEDULE` environment variable like `-e SCHEDULE="@daily"` to run the backup automatically.
 
 More information about the scheduling can be found [here](http://godoc.org/github.com/robfig/cron#hdr-Predefined_schedules).
+

postgres-backup-s3/backup.sh

@@ -23,8 +23,13 @@ if [ "${POSTGRES_DATABASE}" = "**None**" ]; then
 fi
 
 if [ "${POSTGRES_HOST}" = "**None**" ]; then
-  echo "You need to set the POSTGRES_HOST environment variable."
-  exit 1
+  if [ -n "${POSTGRES_PORT_5432_TCP_ADDR}" ]; then
+    POSTGRES_HOST=$POSTGRES_PORT_5432_TCP_ADDR
+    POSTGRES_PORT=$POSTGRES_PORT_5432_TCP_PORT
+  else
+    echo "You need to set the POSTGRES_HOST environment variable."
+    exit 1
+  fi
 fi
 
 if [ "${POSTGRES_USER}" = "**None**" ]; then