Add notes about S3 bucket setup.

README.md

@@ -64,7 +64,7 @@ volumes:
   grafana-data:
 ```
 
-This configuration will back up to AWS S3 instead.
+This configuration will back up to AWS S3 instead. See below for additional tips about [S3 Bucket setup](#s3-bucket-setup).
 
 ### Stopping containers while backing up
 
@@ -177,6 +177,36 @@ If so configured, they can also be shipped to an InfluxDB instance. This allows
 
 ![Backup dashboard sample](doc/backup-dashboard-sample.png)
 
+## S3 Bucket setup
+
+Amazon S3 has [Versioning](https://docs.aws.amazon.com/AmazonS3/latest/dev/Versioning.html) and [Object Lifecycle Management](https://docs.aws.amazon.com/AmazonS3/latest/dev/object-lifecycle-mgmt.html) features that can be useful for backups.
+
+First, you can enable versioning for your backup bucket:
+
+![S3 versioning](doc/s3-versioning.png)
+
+Then, you can change your backup filename to a static one, for example:
+
+```yml
+environment:
+  BACKUP_FILENAME: latest.tar.gz
+```
+
+This allows you to retain previous versions of the backup file, but the _most recent_ version is always available with the same filename:
+
+    $ aws s3 cp s3://my-backup-bucket/latest.tar.gz .
+    download: s3://my-backup-bucket/latest.tar.gz to ./latest.tar.gz
+
+To make sure your bucket doesn't continue to grow indefinitely, you can enable some lifecycle rules:
+
+![S3 lifecycle](doc/s3-lifecycle.png)
+
+These rules will:
+
+- Move non-latest backups to a cheaper, long-term storage class ([Glacier](https://aws.amazon.com/glacier/))
+- Permanently remove backups after a year
+- Still always keep the latest backup available (even after a year has passed)
+
 ## Testing
 
 A bunch of test cases exist under [`test`](test/). To run them:

test/backing-up-to-s3/docker-compose.yml

@@ -13,6 +13,7 @@ services:
     build: ../..
     environment:
       BACKUP_CRON_EXPRESSION: "* * * * *"
+      BACKUP_FILENAME: latest.tar.gz
       AWS_S3_BUCKET_NAME: docker-volume-backup-test-bucket
       AWS_ACCESS_KEY_ID: ${AWS_ACCESS_KEY_ID}
       AWS_SECRET_ACCESS_KEY: ${AWS_SECRET_ACCESS_KEY}