add support for creating backups using pg_basebackup

Changelog.md

@@ -9,6 +9,7 @@
 - added `PG_SSL` parameter to enable/disable SSL support
 - `DB_LOCALE` config parameter renamed to `PG_LOCALE`
 - complete rewrite of the README
+- add support for creating backups using `pg_basebackup`
 
 **9.4-2**
 - added replication options

README.md

@@ -19,6 +19,7 @@
   - [Creating replication user](#creating-replication-user)
   - [Setting up a replication cluster](#setting-up-a-replication-cluster)
   - [Creating a snapshot](#creating-a-snapshot)
+  - [Creating a backup](#creating-a-backup)
   - [Logs](#logs)
   - [UID/GID mapping](#uid-gid-mapping)
 - [Maintenance](#maintenance)
@@ -219,7 +220,7 @@ docker run --name postgresql -itd --restart always \
 > - No changes will be made if the user already exists
 > - Only a single user can be created at each launch
 
-*It is a good idea to create a replication user even if you are not going to use it as it will allow you to setup slave nodes and/or generate snapshots when the need arises.*
+*It is a good idea to create a replication user even if you are not going to use it as it will allow you to setup slave nodes and/or generate snapshots and backups when the need arises.*
 
 ## Setting up a replication cluster
 
@@ -284,6 +285,26 @@ The difference between a slave and a snapshot is that a slave is read-only and u
 
 This is useful for developers to quickly snapshot the current state of a live database and use it for development/debugging purposes without altering the database on the live instance.
 
+## Creating a backup
+
+Just as the case of setting up a slave node or generating a snapshot, you can also create a backup of the data on the master master by specifying `REPLICATION_MODE=backup`.
+
+> The backups are generated using [pg_basebackup](http://www.postgresql.org/docs/9.4/static/app-pgbasebackup.html) using the replication protocol.
+
+Once the master node is created as specified in [Setting up a replication cluster](#setting-up-a-replication-cluster), you can create a point-in-time backup using:
+
+```bash
+docker run --name postgresql-backup -it --rm \
+  --link postgresql-master:master \
+  --env 'REPLICATION_MODE=backup' -e 'REPLICATION_SSLMODE=prefer' \
+  --env 'REPLICATION_HOST=master' -e 'REPLICATION_PORT=5432'  \
+  --env 'REPLICATION_USER=repluser' --env 'REPLICATION_PASS=repluserpass' \
+  --volume /srv/docker/backups/postgresql.$(date +%Y%m%d%H$M%S):/var/lib/postgresql \
+  sameersbn/postgresql:9.4-8
+```
+
+Once the backup is generated, the container will exit and the backup of the master data will be available at `/srv/docker/backups/postgresql.XXXXXXXXXXXX/`. Restoring the backup involves starting a container with the data in `/srv/docker/backups/postgresql.XXXXXXXXXXXX`.
+
 ## Logs
 
 By default the PostgreSQL server logs are sent to the standard output. Using the [Command-line arguments](#command-line-arguments) feature you can configure the PostgreSQL server to send the log output to a file using the `-c logging_collector=on` argument:

runtime/functions

@@ -117,7 +117,7 @@ configure_ssl() {
 
 configure_hot_standby() {
   case ${REPLICATION_MODE} in
-    slave|snapshot) ;;
+    slave|snapshot|backup) ;;
     *)
       echo "Configuring hot standby..."
       set_postgresql_param "wal_level" "hot_standby"
@@ -132,7 +132,7 @@ configure_hot_standby() {
 initialize_database() {
   if [[ ! -f ${PG_DATADIR}/PG_VERSION ]]; then
     case ${REPLICATION_MODE} in
-      slave|snapshot)
+      slave|snapshot|backup)
         # default params
         REPLICATION_PORT=${REPLICATION_PORT:-5432}
         REPLICATION_SSLMODE=${REPLICATION_SSLMODE:-prefer}
@@ -177,6 +177,12 @@ initialize_database() {
             exec_as_postgres PGPASSWORD=$REPLICATION_PASS ${PG_BINDIR}/pg_basebackup -D ${PG_DATADIR} \
               -h ${REPLICATION_HOST} -p ${REPLICATION_PORT} -U ${REPLICATION_USER} -X fetch -w >/dev/null
             ;;
+          backup)
+            echo "Backing up data on $REPLICATION_HOST..."
+            exec_as_postgres PGPASSWORD=$REPLICATION_PASS ${PG_BINDIR}/pg_basebackup -D ${PG_DATADIR} \
+              -h ${REPLICATION_HOST} -p ${REPLICATION_PORT} -U ${REPLICATION_USER} -X fetch -w >/dev/null
+            exit 0
+            ;;
         esac
         ;;
       *)
@@ -289,7 +295,7 @@ create_database() {
 
 create_replication_user() {
   case $REPLICATION_MODE in
-    slave|snapshot) ;; # replication user can only be created on the master
+    slave|snapshot|backup) ;; # replication user can only be created on the master
     *)
       if [[ -n ${REPLICATION_USER} ]]; then
         if [[ -z ${REPLICATION_PASS} ]]; then