Running cron in AWS ElasticBeanstalk web tier.

cron.conf

files:
  "/tmp/crontab":
    mode: "000777"
    owner: 'ec2-user'
    group: 'ec2-user'
    content: |
      30 02 * * * sudo /usr/sbin/execute-in-eb-node-app 'node bin/is-eb-master.js' && sudo /usr/sbin/execute-in-eb-node-app 'npm run daily-maintenance'
    encoding: plain
container_commands:
  01-copy_eb_bin:
    command: 'cp -f ./.ebextensions/bin/eb-is-master.js ./bin/'
  02-copy_eb_sbin:
    command: 'sudo cp -f ./.ebextensions/sbin/execute-in-eb-node-app.sh /usr/sbin/execute-in-eb-node-app'
commands:
  01-load_crontab:
    command: 'sudo crontab /tmp/crontab'
  02-remove_crontab_file:
    command: 'rm /tmp/crontab'

execute-in-eb-node-app.sh

#!/bin/bash

# Execute node command with EB's node.js environment.
# Basically, /etc/init/nodejs.conf defines how node command is executed:
#  - environment variables
#  - add path to node.js installation
#  - execute as nodejs user
# Implementation is taken from https://github.com/kopurando/better-faster-elastic-beanstalk/blob/7e20fe7/cron-node.sh
# Note: requires root access.

eval "$(grep -E '^env [A-Za-z0-9_-]+="[^"]+"$' /etc/init/nodejs.conf |  sed 's/env /export /g')"
export __EXECUTE_NODE_COMMAND="$1"
cd /var/app/current
exec su -s /bin/sh -c 'PATH=$PATH:$NODE_HOME/bin eval "$__EXECUTE_NODE_COMMAND" 2>&1' nodejs

is-eb-master.js

#!/usr/bin/env node

"use strict";

const checkWhetherEbMasterInstance = require_checkWhetherEbMasterInstance();

checkWhetherEbMasterInstance().then(isMaster => {
    process.exit(isMaster ? 0 : 1);
}).catch(err => {
    console.log(err);
    console.log(err.stack);
    process.exit(1);
});


// https://gist.github.com/ippeiukai/e12b2cd3ae6424d220f2a802443e5548
function require_checkWhetherEbMasterInstance() {
    let module = {exports: {}};
    (function (module) {
"use strict";

const AWS = require('aws-sdk');
const bluebird = require('bluebird');

/**
 * @returns {Promise.<boolean>} - is on 'master' instance or not 
 */
module.exports = bluebird.coroutine(function* (opts) {
    if (opts == null) {
        opts = {
            // default to use the credentials for the ec2 instance
            credentials: new AWS.EC2MetadataCredentials(),
        };
    }

    let instanceId = yield findCurrentInstanceId(opts);
    let beanstalkEnvironmentId = yield findEbEnvironmentId(instanceId, opts);
    let instanceIds = yield findEbInstanceIds(beanstalkEnvironmentId, opts);

    // first in the list is the master
    return instanceId === instanceIds[0]
});


const findCurrentInstanceId = function (opts) {
    return requestMatadata('/latest/meta-data/instance-id', opts)
};

const findEbEnvironmentId = function (instanceId, opts) {
    let params = {
        Filters: [
            {
                Name: "resource-id",
                Values: [
                    instanceId,
                ]
            }
        ]
    };
    return requestEc2Tags(params, opts).then(tags => {
        let envIdTag = tags.find(t => t.Key === 'elasticbeanstalk:environment-id');
        if (envIdTag == null) {
            return Promise.reject(new Error('failed to find the value of "elasticbeanstalk:environment-id" tag.'));
        }
        return envIdTag.Value
    })
};

const findEbInstanceIds = function (environmentId, opts) {
    let params = {
        EnvironmentId: environmentId
    };
    return requestEbEnvironmentResources(params, opts)
        .then(envResources => envResources.Instances.map(it => it.Id))
};


const promisifyMethod = function (obj, name) {
    return bluebird.promisify(obj[name], {context: obj})
};

const requestMatadata = function (path, opts) {
    let metadata = new AWS.MetadataService(opts);
    return promisifyMethod(metadata, 'request')(path)
};

const requestEc2Tags = function (params, opts) {
    let ec2 = new AWS.EC2(opts);
    return promisifyMethod(ec2, 'describeTags')(params).then(data => data.Tags);
};

const requestEbEnvironmentResources = function (params, opts) {
    let elasticbeanstalk = new AWS.ElasticBeanstalk(opts);
    return promisifyMethod(elasticbeanstalk, 'describeEnvironmentResources')(params)
        .then(data => data.EnvironmentResources)
};

    })(module);
    return module.exports
}