added wal-g example to docs

doc/README.md

@@ -12,6 +12,7 @@ We suggest that you first read the [Stolon Architecture and Requirements](archit
 * Backup/Restore
   * [Point In Time Recovery](pitr.md)
   * [Point In Time Recovery with wal-e](pitr_wal-e.md)
+  * [Point In Time Recovery with wal-g](pitr_wal-g.md)
 * [Standby Cluster](standbycluster.md)
 
 ### Misc topics

doc/pitr.md

@@ -1,7 +1,9 @@
 ## Point in time recovery
 
 Stolon can do a point a time recovery starting from an existing backup.
-This example shows how to do point in time recovery with stolon using [wal-e](https://github.com/wal-e/wal-e)
+
+* [This](pitr_wal-g.md) example shows how to do point in time recovery with stolon using [wal-g](https://github.com/wal-g/wal-g)
+* [This](pitr_wal-e.md) example shows how to do point in time recovery with stolon using [wal-e](https://github.com/wal-e/wal-e)
 
 
 ### Backups

doc/pitr_wal-g.md

@@ -0,0 +1,33 @@
+## Point in time recovery with wal-g
+
+[wal-g](https://github.com/wal-g/wal-g) is the successor of wal-e, which no longer seems to be in active development!
+This example shows how to do point in time recovery with stolon using [wal-g](https://github.com/wal-g/wal-g)
+
+[wal-g](https://github.com/wal-g/wal-g) correctly suggests to not put environment variables containing secret data (like aws secret keys) inside the `archive_command` since every user connected to postgres could read them. In its examples wal-g suggests to use the `envdir` command to set the wal-g required environment variables or (since some distribution don't have it) just use a custom script that sets them.
+
+### Backups
+
+#### Base backups
+
+Take the base backups using the `wal-g backup-push` command.
+
+#### Archive backups
+
+For doing this you should set at least the `archive_mode` and the `archive_command` pgParameters in the cluster spec. Wal-g will be used as the archive command:
+
+```
+stolonctl update --patch '{ "pgParameters" : { "archive_mode": "on", "archive_command": "envdir /etc/wal-g.d/env wal-g wal-push %p" } }'
+```
+
+
+### Execute a point in time recovery
+
+Note: looks like wal-g doesn't backups various config files like `postgresql.conf`, `pg_hba.conf`. While `pg_hba.conf` is currently generated by stolon, you'd like to keep the previous postgres parameters after the restore. For doing this there're two different ways:
+
+* if you want to backup the `postgresql.conf` you should do this outside `wal-g`.  To restore it you have to create a `dataRestoreCommand` that will restore it after the `wal-g backup fetch` command.
+* if you don't want to backup/restore it than you can just set all the `pgParameters` inside the [cluster specification](cluster_spec.md)
+
+```
+stolonctl init '{ "initMode": "pitr", "pitrConfig": { "dataRestoreCommand": "envdir /etc/wal-g.d/env wal-g backup-fetch %d LATEST" , "archiveRecoverySettings": { "restoreCommand": "envdir /etc/wal-g.d/env wal-g wal-fetch \"%f\" \"%p\"" } } }'
+```
+