Switch to cron for scheduling.

Dockerfile

@@ -1,12 +1,15 @@
 FROM ubuntu:18.04
 
-RUN apt-get update && apt-get install -y curl awscli
+RUN apt-get update && apt-get install -y curl cron awscli
 
 # https://docs.docker.com/engine/installation/linux/docker-ce/ubuntu/#install-using-the-convenience-script
 RUN curl -fsSL get.docker.com -o get-docker.sh
 RUN sh get-docker.sh
 
+COPY ./entrypoint.sh /root/
 COPY ./backup.sh /root/
+RUN chmod a+x /root/entrypoint.sh
 RUN chmod a+x /root/backup.sh
 
-CMD [ "/root/backup.sh" ]
+WORKDIR /root
+CMD [ "/root/entrypoint.sh" ]

backup.sh

@@ -3,17 +3,8 @@
 # Exit immediately on error
 set -e
 
-# Set defaults for any missing environment variables
-BACKUP_SOURCES="${BACKUP_SOURCES:-/backup}"
-BACKUP_FILENAME="${BACKUP_FILENAME:-latest.tar.gz}"
-BACKUP_PERIOD_SECONDS="${BACKUP_PERIOD_SECONDS:-86400}" # i.e. every 24 hours
-BACKUP_UPLOAD_WAIT_SECONDS="${BACKUP_UPLOAD_WAIT_SECONDS:-30}" # to wait out the load spike of starting the containers back up
-BACKUP_HOSTNAME="${BACKUP_HOSTNAME:-$(hostname)}"
-DOCKER_STOP_OPT_IN_LABEL="${DOCKER_STOP_OPT_IN_LABEL:-docker-volume-backup-companion.stop-during-backup}"
-INFLUXDB_URL="${INFLUXDB_URL:-}"
-INFLUXDB_DB="${INFLUXDB_DB:-}"
-INFLUXDB_CREDENTIALS="${INFLUXDB_CREDENTIALS:-}"
-INFLUXDB_MEASUREMENT="${INFLUXDB_MEASUREMENT:-docker_volume_backup}"
+# Cronjobs don't inherit their env, so load from file
+source env.sh
 
 function info {
   bold="\033[1m"
@@ -21,10 +12,6 @@ function info {
   echo -e "\n$bold[INFO] $1\n$reset"
 }
 
-info "Backup sleeping"
-echo "Sleeping $BACKUP_PERIOD_SECONDS seconds..."
-sleep "$BACKUP_PERIOD_SECONDS"
-
 info "Backup starting"
 TIME_START="$(date +%s.%N)"
 CONTAINERS_TO_STOP="$(docker ps --format "{{.ID}}" --filter "label=$DOCKER_STOP_OPT_IN_LABEL=true" | tr '\n' ' ')"

entrypoint.sh

@@ -0,0 +1,41 @@
+#!/bin/bash
+
+# Exit immediately on error
+set -e
+
+# Write cronjob env to file, fill in sensible defaults, and read them back in
+cat <<EOF > env.sh
+BACKUP_SOURCES="${BACKUP_SOURCES:-/backup}"
+BACKUP_CRON_EXPRESSION="${BACKUP_CRON_EXPRESSION:-@daily}"
+BACKUP_BUCKET_NAME="${BACKUP_BUCKET_NAME:-}"
+BACKUP_FILENAME="${BACKUP_FILENAME:-latest.tar.gz}"
+BACKUP_UPLOAD_WAIT_SECONDS="${BACKUP_UPLOAD_WAIT_SECONDS:-30}"
+BACKUP_HOSTNAME="${BACKUP_HOSTNAME:-$(hostname)}"
+DOCKER_STOP_OPT_IN_LABEL="${DOCKER_STOP_OPT_IN_LABEL:-docker-volume-backup-companion.stop-during-backup}"
+INFLUXDB_URL="${INFLUXDB_URL:-}"
+INFLUXDB_DB="${INFLUXDB_DB:-}"
+INFLUXDB_CREDENTIALS="${INFLUXDB_CREDENTIALS:-}"
+INFLUXDB_MEASUREMENT="${INFLUXDB_MEASUREMENT:-docker_volume_backup}"
+EOF
+chmod a+x env.sh
+source env.sh
+
+# Configure AWS CLI
+mkdir .aws
+cat <<EOF > .aws/credentials
+[default]
+aws_access_key_id = ${AWS_ACCESS_KEY_ID}
+aws_secret_access_key = ${AWS_SECRET_ACCESS_KEY}
+EOF
+cat <<EOF > .aws/config
+[default]
+region = ${AWS_DEFAULT_REGION}
+EOF
+
+# Add our cron entry, and direct stdout & stderr to Docker commands stdout
+echo "Installing cron.d entry: docker-volume-backup-companion"
+echo "$BACKUP_CRON_EXPRESSION root /root/backup.sh > /proc/1/fd/1 2>&1" > /etc/cron.d/docker-volume-backup-companion
+
+# Let cron take the wheel
+echo "Starting cron in foreground with expression: $BACKUP_CRON_EXPRESSION"
+cron -f