How to run a crontab job on elastic search docker image - docker

Question

I want to run a crontab job on elastic search docker image and here is my docker file
FROM docker.elastic.co/elasticsearch/elasticsearch:6.6.0
ENV PATH=$PATH:/usr/share/elasticsearch/bin
RUN yum -y update
RUN yum -y install crontabs
RUN echo -e "root\nelasticsearch" > /etc/cron.allow
RUN echo "" >> /etc/cron.allow
RUN chmod -R 644 /etc/cron.d
RUN cat /etc/cron.allow
RUN chown -R elasticsearch /etc/cron.d
RUN chmod -R 755 /etc/cron.d
RUN chown -R elasticsearch /var/spool/cron
RUN chmod -R 744 /var/spool/cron
RUN chown -R elasticsearch /etc/crontab
RUN chmod -R 744 /etc/crontab
RUN chown -R elasticsearch /etc/cron.d
RUN chmod -R 744 /etc/cron.d
COPY ./purge.sh /usr/share/elasticsearch
RUN ls -l /etc/crontab
RUN ls -l /etc/cron.d
RUN touch /usr/share/elasticsearch/cron.log
ADD ./cron /etc/cron.d/cron_test
RUN chmod 0644 /etc/cron.d/cron_test
RUN cd /etc/cron.d && cat cron_test
RUN chown -R elasticsearch /etc/cron.d/cron_test
RUN ls -l /etc/cron.d/cron_test
RUN crontab /etc/cron.d/cron_test
RUN crontab -l
RUN cd /var/spool/cron && ls
USER elasticsearch
ENTRYPOINT elasticsearch
CMD crond start && pgrep cron && tail -f && tail -f /usr/share/elasticsearch/cron.log
EXPOSE 9200 9300
after running this docker file and executing the container, i am getting this
enter image description here
In this step in docker file
RUN cd /var/spool/cron && ls
it's showing only root , but how can i get elasticsearch user in it ?**
my cron file present locally
*/1 * * * * echo "Hello world" >> /usr/share/elasticsearch/cron.log
*/1 * * * * elasticsearch /usr/share/elasticsearch/purge.sh
my purge.sh file
curl -XPOST "http://localhost:9200/hydro_dashboard_index/_delete_by_query" -H 'Content-Type: application/json' -d'
{
"query": {
"range" : {
"query_service_entry_time" : {
"lt" : "now-14d"
}
}
}
}'

Answer 1

It's usually considered a better practice to run only one process in a container. Since the thing you're trying to run in cron is just making an HTTP request to elasticsearch, there's nothing about it that needs to run in the same container, or even in Docker at all.
If your host is running a standard Linux distribution with a standard cron daemon, the absolute easiest thing to do is just to stash this purge script somewhere on your host and run it via the host's cron service. If you know cron and elasticsearch are on the same host and you start the container with a -p 9200:9200 option to publish the standard elasticsearch HTTP port, the script should work unmodified.
If absolutely everything must run in Docker, you might search Docker Hub for a prebuilt cron image (there are a couple, though none look especially actively maintained). You also might be able to use the minimal set of tools in the busybox image; its documentation can be a little light. Still, the basic approach you'd need to take looks like:
Find or build a Docker image that contains only cron and curl – no Elasticsearch, no actual crontabs, just the programs themselves.
If you're manually docker running containers, docker network create some_network (with any name and default options), and run both the Elasticsearch and cron containers with --net some_network.
In the curl commands, use the docker run --name of the Elasticsearch container, or the name of its Docker Compose services: block, as a hostname; localhost will always mean "this container".
Put the crontabs and support scripts in some directory on your host, and inject them into the cron container with the docker run -v option (that is, treat them as configuration).