Add support to launch initial backups on startup

Author: prodrigestivill

README.md

@@ -51,6 +51,7 @@ services:
          #  - POSTGRES_PASSWORD_FILE=/run/secrets/db_password <-- alternative for POSTGRES_PASSWORD (to use with docker secrets)
             - POSTGRES_EXTRA_OPTS=-Z1 --schema=public --blobs
             - SCHEDULE=@daily
+            - INITIAL_BACKUP=TRUE
             - BACKUP_KEEP_DAYS=7
             - BACKUP_KEEP_WEEKS=4
             - BACKUP_KEEP_MONTHS=6
@@ -93,6 +94,7 @@ Most variables are the same as in the [official postgres image](https://hub.dock
 | POSTGRES_USER | Postgres connection parameter; postgres user to connect with. Required. |
 | POSTGRES_USER_FILE | Alternative to POSTGRES_USER, for usage with docker secrets. |
 | SCHEDULE | [Cron-schedule](http://godoc.org/github.com/robfig/cron#hdr-Predefined_schedules) specifying the interval between postgres backups. Defaults to `@daily`. |
+| INITIAL_BACKUP | If set to `TRUE` performs an initial backup. Defaults to `FALSE`. |
 | TZ | [POSIX TZ variable](https://www.gnu.org/software/libc/manual/html_node/TZ-Variable.html) specifying the timezone used to evaluate SCHEDULE cron (example "Europe/Paris"). |
 | WEBHOOK_URL | URL to be called after an error or after a successful backup (POST with a JSON payload, check `hooks/00-webhook` file for more info). Default disabled. |
 | WEBHOOK_ERROR_URL | URL to be called in case backup fails. Default disabled. |

alpine.Dockerfile

@@ -21,6 +21,7 @@ ENV POSTGRES_DB="**None**" \
     POSTGRES_EXTRA_OPTS="-Z1" \
     POSTGRES_CLUSTER="FALSE" \
     SCHEDULE="@daily" \
+    INITIAL_BACKUP="FALSE" \
     BACKUP_DIR="/backups" \
     BACKUP_SUFFIX=".sql.gz" \
     BACKUP_LATEST_TYPE="symlink" \

debian.Dockerfile

@@ -35,6 +35,7 @@ ENV POSTGRES_DB="**None**" \
     POSTGRES_EXTRA_OPTS="-Z1" \
     POSTGRES_CLUSTER="FALSE" \
     SCHEDULE="@daily" \
+    INITIAL_BACKUP="FALSE" \
     BACKUP_DIR="/backups" \
     BACKUP_SUFFIX=".sql.gz" \
     BACKUP_LATEST_TYPE="symlink" \

init.sh

@@ -4,4 +4,11 @@ set -Eeo pipefail
 # Prevalidate configuration (don't source)
 /env.sh
 
+# Initial background backup
+if [ "${INITIAL_BACKUP}" = "TRUE" ]; then
+  echo "Launching an initial backup as a background job..."
+  /backup.sh &
+fi
+
+echo "Starting go-cron ($SCHEDULE)..."
 exec /usr/local/bin/go-cron -s "$SCHEDULE" -p "$HEALTHCHECK_PORT" -- /backup.sh