now using supercronic instead of cron

Author: Julien Neuhart

Dockerfile.10

@@ -10,7 +10,24 @@ LABEL authors="Julien Neuhart <j.neuhart@thecodingmachine.com>, David Négrier <
 # |
 
 RUN apt-get update &&\
-    apt-get install -y --no-install-recommends curl cron git nano sudo ca-certificates procps --no-install-recommends
+    apt-get install -y --no-install-recommends curl git nano sudo ca-certificates procps --no-install-recommends
+
+# |--------------------------------------------------------------------------
+# | Supercronic
+# |--------------------------------------------------------------------------
+# |
+# | Supercronic is a drop-in replacement for cron (for containers).
+# |
+
+RUN SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.5/supercronic-linux-amd64 \
+ && SUPERCRONIC=supercronic-linux-amd64 \
+ && SUPERCRONIC_SHA1SUM=9aeb41e00cc7b71d30d33c57a2333f2c2581a201 \
+ && curl -fsSLO "$SUPERCRONIC_URL" \
+ && echo "${SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
+ && chmod +x "$SUPERCRONIC" \
+ && mv "$SUPERCRONIC" "/usr/local/bin/${SUPERCRONIC}" \
+ && ln -s "/usr/local/bin/${SUPERCRONIC}" /usr/local/bin/supercronic
+
 
 
 

Dockerfile.10-apache

@@ -10,7 +10,24 @@ LABEL authors="Julien Neuhart <j.neuhart@thecodingmachine.com>, David Négrier <
 # |
 
 RUN apt-get update &&\
-    apt-get install -y --no-install-recommends curl cron git nano sudo ca-certificates procps --no-install-recommends
+    apt-get install -y --no-install-recommends curl git nano sudo ca-certificates procps --no-install-recommends
+
+# |--------------------------------------------------------------------------
+# | Supercronic
+# |--------------------------------------------------------------------------
+# |
+# | Supercronic is a drop-in replacement for cron (for containers).
+# |
+
+RUN SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.5/supercronic-linux-amd64 \
+ && SUPERCRONIC=supercronic-linux-amd64 \
+ && SUPERCRONIC_SHA1SUM=9aeb41e00cc7b71d30d33c57a2333f2c2581a201 \
+ && curl -fsSLO "$SUPERCRONIC_URL" \
+ && echo "${SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
+ && chmod +x "$SUPERCRONIC" \
+ && mv "$SUPERCRONIC" "/usr/local/bin/${SUPERCRONIC}" \
+ && ln -s "/usr/local/bin/${SUPERCRONIC}" /usr/local/bin/supercronic
+
 
 
 # |--------------------------------------------------------------------------

Dockerfile.6

@@ -10,7 +10,24 @@ LABEL authors="Julien Neuhart <j.neuhart@thecodingmachine.com>, David Négrier <
 # |
 
 RUN apt-get update &&\
-    apt-get install -y --no-install-recommends curl cron git nano sudo ca-certificates procps --no-install-recommends
+    apt-get install -y --no-install-recommends curl git nano sudo ca-certificates procps --no-install-recommends
+
+# |--------------------------------------------------------------------------
+# | Supercronic
+# |--------------------------------------------------------------------------
+# |
+# | Supercronic is a drop-in replacement for cron (for containers).
+# |
+
+RUN SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.5/supercronic-linux-amd64 \
+ && SUPERCRONIC=supercronic-linux-amd64 \
+ && SUPERCRONIC_SHA1SUM=9aeb41e00cc7b71d30d33c57a2333f2c2581a201 \
+ && curl -fsSLO "$SUPERCRONIC_URL" \
+ && echo "${SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
+ && chmod +x "$SUPERCRONIC" \
+ && mv "$SUPERCRONIC" "/usr/local/bin/${SUPERCRONIC}" \
+ && ln -s "/usr/local/bin/${SUPERCRONIC}" /usr/local/bin/supercronic
+
 
 
 

Dockerfile.6-apache

@@ -10,7 +10,24 @@ LABEL authors="Julien Neuhart <j.neuhart@thecodingmachine.com>, David Négrier <
 # |
 
 RUN apt-get update &&\
-    apt-get install -y --no-install-recommends curl cron git nano sudo ca-certificates procps --no-install-recommends
+    apt-get install -y --no-install-recommends curl git nano sudo ca-certificates procps --no-install-recommends
+
+# |--------------------------------------------------------------------------
+# | Supercronic
+# |--------------------------------------------------------------------------
+# |
+# | Supercronic is a drop-in replacement for cron (for containers).
+# |
+
+RUN SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.5/supercronic-linux-amd64 \
+ && SUPERCRONIC=supercronic-linux-amd64 \
+ && SUPERCRONIC_SHA1SUM=9aeb41e00cc7b71d30d33c57a2333f2c2581a201 \
+ && curl -fsSLO "$SUPERCRONIC_URL" \
+ && echo "${SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
+ && chmod +x "$SUPERCRONIC" \
+ && mv "$SUPERCRONIC" "/usr/local/bin/${SUPERCRONIC}" \
+ && ln -s "/usr/local/bin/${SUPERCRONIC}" /usr/local/bin/supercronic
+
 
 
 # |--------------------------------------------------------------------------

Dockerfile.8

@@ -10,7 +10,24 @@ LABEL authors="Julien Neuhart <j.neuhart@thecodingmachine.com>, David Négrier <
 # |
 
 RUN apt-get update &&\
-    apt-get install -y --no-install-recommends curl cron git nano sudo ca-certificates procps --no-install-recommends
+    apt-get install -y --no-install-recommends curl git nano sudo ca-certificates procps --no-install-recommends
+
+# |--------------------------------------------------------------------------
+# | Supercronic
+# |--------------------------------------------------------------------------
+# |
+# | Supercronic is a drop-in replacement for cron (for containers).
+# |
+
+RUN SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.5/supercronic-linux-amd64 \
+ && SUPERCRONIC=supercronic-linux-amd64 \
+ && SUPERCRONIC_SHA1SUM=9aeb41e00cc7b71d30d33c57a2333f2c2581a201 \
+ && curl -fsSLO "$SUPERCRONIC_URL" \
+ && echo "${SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
+ && chmod +x "$SUPERCRONIC" \
+ && mv "$SUPERCRONIC" "/usr/local/bin/${SUPERCRONIC}" \
+ && ln -s "/usr/local/bin/${SUPERCRONIC}" /usr/local/bin/supercronic
+
 
 
 

Dockerfile.8-apache

@@ -10,7 +10,24 @@ LABEL authors="Julien Neuhart <j.neuhart@thecodingmachine.com>, David Négrier <
 # |
 
 RUN apt-get update &&\
-    apt-get install -y --no-install-recommends curl cron git nano sudo ca-certificates procps --no-install-recommends
+    apt-get install -y --no-install-recommends curl git nano sudo ca-certificates procps --no-install-recommends
+
+# |--------------------------------------------------------------------------
+# | Supercronic
+# |--------------------------------------------------------------------------
+# |
+# | Supercronic is a drop-in replacement for cron (for containers).
+# |
+
+RUN SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.5/supercronic-linux-amd64 \
+ && SUPERCRONIC=supercronic-linux-amd64 \
+ && SUPERCRONIC_SHA1SUM=9aeb41e00cc7b71d30d33c57a2333f2c2581a201 \
+ && curl -fsSLO "$SUPERCRONIC_URL" \
+ && echo "${SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
+ && chmod +x "$SUPERCRONIC" \
+ && mv "$SUPERCRONIC" "/usr/local/bin/${SUPERCRONIC}" \
+ && ln -s "/usr/local/bin/${SUPERCRONIC}" /usr/local/bin/supercronic
+
 
 
 # |--------------------------------------------------------------------------

README.md

@@ -162,7 +162,8 @@ CRON_SCHEDULE_2=0 3 * * *
 CRON_COMMAND_2=yarn run other-stuff
 ```
 
-**Important**: Cron was never designed with Docker in mind (it is way older than Docker). It will run correctly on
+**Important**: The cron runner we use is "Supercronic" and not the orginial "cron" that has a number of issues with containers. 
+Even with Supercronic, the architecture of cron was never designed with Docker in mind (Cron is way older than Docker). It will run correctly on
 your container. If at some point you want to scale and add more containers, it will run on all your containers.
 At that point, if you only want to run a Cron task once for your application (and not once per container), you might
 want to have a look at alternative solutions like [Tasker](https://github.com/opsxcq/tasker) or one of the many

utils/Dockerfile.blueprint

@@ -13,7 +13,24 @@ LABEL authors="Julien Neuhart <j.neuhart@thecodingmachine.com>, David Négrier <
 # |
 
 RUN apt-get update &&\
-    apt-get install -y --no-install-recommends curl cron git nano sudo ca-certificates procps --no-install-recommends
+    apt-get install -y --no-install-recommends curl git nano sudo ca-certificates procps --no-install-recommends
+
+# |--------------------------------------------------------------------------
+# | Supercronic
+# |--------------------------------------------------------------------------
+# |
+# | Supercronic is a drop-in replacement for cron (for containers).
+# |
+
+RUN SUPERCRONIC_URL=https://github.com/aptible/supercronic/releases/download/v0.1.5/supercronic-linux-amd64 \
+ && SUPERCRONIC=supercronic-linux-amd64 \
+ && SUPERCRONIC_SHA1SUM=9aeb41e00cc7b71d30d33c57a2333f2c2581a201 \
+ && curl -fsSLO "$SUPERCRONIC_URL" \
+ && echo "${SUPERCRONIC_SHA1SUM}  ${SUPERCRONIC}" | sha1sum -c - \
+ && chmod +x "$SUPERCRONIC" \
+ && mv "$SUPERCRONIC" "/usr/local/bin/${SUPERCRONIC}" \
+ && ln -s "/usr/local/bin/${SUPERCRONIC}" /usr/local/bin/supercronic
+
 
 {{ if eq $variant "apache" }}
 # |--------------------------------------------------------------------------

utils/docker-entrypoint-as-root.sh

@@ -47,16 +47,19 @@ fi
 DOCKER_USER_ID=`id -ur $DOCKER_USER`
 #echo "Docker user id: $DOCKER_USER_ID"
 
-# output on the logs can be done by writing on the "tini" PID. Useful for CRONTAB
-TINI_PID=`ps -e | grep tini | awk '{print $1;}'`
-node /usr/local/bin/generate_cron.js $TINI_PID > /etc/cron.d/generated_crontab
-chmod 0644 /etc/cron.d/generated_crontab
-
 if [[ "$IMAGE_VARIANT" == "apache" ]]; then
     node /usr/local/bin/enable_apache_mods.js | bash
 fi
 
-cron
+# output on the logs can be done by writing on the "tini" PID. Useful for CRONTAB
+TINI_PID=`ps -e | grep tini | awk '{print $1;}'`
+node /usr/local/bin/generate_cron.js $TINI_PID > /tmp/generated_crontab
+chmod 0644 /tmp/generated_crontab
+
+# If generated_crontab is not empty, start supercronic
+if [[ -s /tmp/generated_crontab ]]; then
+    supercronic /tmp/generated_crontab &
+fi
 
 if [ -e /etc/container/startup.sh ]; then
     sudo -E -u "#$DOCKER_USER_ID" source /etc/container/startup.sh

utils/generate_cron.js

@@ -3,8 +3,7 @@
  * The script is run on each start of the container.
  */
 
-let tiniPid = process.argv[2],
-    envVars = Object.keys(process.env);
+let envVars = Object.keys(process.env);
 
 envVars.forEach((envVar) => {
     if (envVar.indexOf('CRON_COMMAND') >= 0) {
@@ -19,13 +18,10 @@ envVars.forEach((envVar) => {
         let user = envVars.indexOf('CRON_USER' + suffix) >= 0 ? process.env['CRON_USER' + suffix] : 'root',
             schedule = process.env['CRON_SCHEDULE' + suffix];
 
-        // Note: this is a bit cryptic so here is what is going on:
-        // First the command is piped into "sed" and we add [Cron]
-        // In case there is an error message (on stderr), this will not be handled by sed.
-        // So we switch output and error streams using "3>&2 2>&1 1>&3"
-        // And we apply again sed on stdout (which is the past stderr)
-        // Finally we switch back to stderr and stdout: 4>&2 2>&1 1>&4
-        // and we put the output in /proc/xxx/fd1|2 which are the processes output for the Docker container.
-        console.log(schedule + ' ' + user + ' ((((' + command + ") | sed -e 's/^/[Cron] /' ) 3>&2 2>&1 1>&3 | sed -e 's/^/[Cron error] /') 4>&2 2>&1 1>&4) > /proc/" + tiniPid + "/fd/1 2> /proc/" + tiniPid + "/fd/2");
+        if (user !== 'root') {
+            command = 'sudo -E -u ' + user + ' ' + command;
+        }
+
+        console.log(schedule + ' ' + command);
     }
 });