wale_postgres_recovery.md

A quick "how to" on what you need to do to both setup AND recover a single-server PostgreSQL database using WAL-E

• WAL-E: https://github.com/wal-e/wal-e
• Assuming Ubuntu 12.04 LTS ("Precise")
• We'll be using S3. Make sure you have an IAM user with

Setup:

1. These packages:

$ sudo apt-get install daemontools libevent-dev python-all-dev lzop pv
$ sudo easy_install pip
$ sudo pip install wal-e

Notes: daemontools provides us with the envdir program, which lets us (safely) store sensitive keys as environmental variables. We'll use it to store our S3 credentials.

2. An S3 bucket (i.e. /myservice/pg-backups)
3. An S3 user that can (at a minimum) GetObject, ListBucket and PutObject. I'd suggest turning on versioning on the bucket and adding GetObjectVersion to that list too. That'll make sure server compromise won't allow someone to overwrite the backups you made[3]
4. Set up your access keys:

$ mkdir -p /etc/wal-e.d/env
$ echo "YOUR_AWS_ACCESS_KEY" > /etc/wal-e.d/env/AWS_ACCESS_KEY_ID
$ echo "YOUR_AWS_SECRET" > /etc/wal-e.d/env/AWS_SECRET_ACCESS_KEY
$ echo 's3://myservice/pg-backups' >  /etc/wal-e.d/env/WALE_S3_PREFIX
$ chown -R root:postgres /etc/wal-e.d

5. Uncomment and modify these lines in your postgresql.conf file under /etc/postgresql/9.3/main/

wal_level = archive
archive_mode = on
archive_command = 'envdir /etc/wal-e.d/env /usr/local/bin/wal-e wal-push %p'
archive_timeout = 60

Note: Make sure to use the full path to wal-e so that PostgreSQL can find it.

Now we're ready to make our first backup. You can also set the PGDATA environmental variable to the location of your PostgreSQL data dir (/var/lib/postgresql/9.3/main on Ubuntu/Debian) either as a shell variable or using envdir like we did for the AWS keys.

Pushing Backups:

1. Make sure you're the postgres user (the default user PostgreSQL runs as) with sudo su - postgres
2. Create our first full backup, which is the reference point for our WAL logs with the following:
   envdir /etc/wal-e.d/env /usr/local/bin/wal-e backup-push /var/lib/postgresql/9.3/main
3. We can check the list of full backups with envdir /etc/wal-e.d/env /usr/local/bin/wal-e backup-list

You can also delete older backups with wal-e delete [--confirm] before <base_XXXX> where <base_XXX> is from backup-list. Make sure to double check the dates on the backups.

Fetching a Backup:

We'll assume worst-case here: you have a blank machine with everything as it was except your data. Postgres has been re-installed as before and you're now wanting to recover your database.

Note: Make sure to read the WAL-E docs on user-created tablespaces and how that interacts with fetches first.

1. Make sure PostgreSQL isn't running and change to the postgres user.
2. Delete the default data directory as the restore process will re-create it.

$ rm -r /var/lib/postgresql/9.3/main // (under Ubuntu/Debian)

3. Fetch the latest backup. You can replace LATEST with the name of a specific backup as identified from backup-list:

$ envdir /etc/wal-e.d/env /usr/local/bin/wal-e backup-fetch /var/lib/postgresql/9.3/main LATEST

4. Ensure the permissions are correct:

$ chown -R postgres:postgres /var/lib/postgresql/9.3/main
$ chmod 0700 /var/lib/postgresql/9.3/main

5. Create a recovery.conf within /var/lib/postgresql/9.3/main/ with the following contents:

restore_command = '/usr/bin/envdir /etc/wal-e.d/env /usr/local/bin/wal-e wal-fetch "%f" "%p"'

6. Start your PostgreSQL server. It might take a little while (it will replay the the WAL files on top of your specified base backup). The recovery.conf file will be renamed to recovery.done once the process is complete.
7. Get back to work (read: check your data is there!)

References:

• [1] https://gist.github.com/ruckus/2293434
• [2] https://coderwall.com/p/cwe2_a
• [3] http://blog.opbeat.com/2013/01/07/postgresql-backup-to-s3-part-one/