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Cannot build a working docker image for an openldap service

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Giorgio Mossa

I'm new to docker and I'm doing a little bit of experimenting with it.

I was trying to create a docker image for an openldap service. I tried creating the image starting from debian:latest image provided from the official docker repos.

This is the content of my Dockerfile

FROM debian
RUN DEBIAN_FRONTEND="noninteractive" apt-get update
RUN DEBIAN_FRONTEND="noninteractive" apt-get install --yes --no-install-recommends slapd ldap-utils
RUN apt-get clean

I tried to create a container based on this image with

docker container run --interactive --tty --name=prova image

here image is the name of the image build from the Dockerfile above. When I try to run slapd with service slapd start I get the following error:

[614.896012] Out of memory: Killed process 4005 (slapd) total-vm: 795276KB, anon-rss:334664KB, file-rss:8KB, shmem-rss:0kB, UID:101, pgtables:1108kB, oom_score_adj:0

So it seems to be a kernel error, due to explosion of the process inside the memory, though I cannot understand what causes it, the same ldap service works fine in the host system or in kvm virtual machines I created.
I've also tried to install openldap inside a live container created from the debian:latest image, I get the same error.

So here's my question: can anyone explain what is going on here and what it's causing the error? Thanks for your help.

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Otto

Running service slapd start inside a docker container will probably waste some resources, in you case memory, since it needs to run the initd and some shell processes, thus triggering oom-killer quicker than single process container.

You can check the Dockerfile from a well used openldap docker image [1], which runs slapd process directly.

If you are preparing an image for production use, you should also think about Backups and TLS, which are supported by osixia/docker-openldap [1] and docker-openldap-backup [2]

[1] https://github.com/osixia/docker-openldap

[2] https://github.com/osixia/docker-openldap-backup

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Giorgio Mossa
Thanks a lot. Actually reading in osixia's repo I find out a reference describing the problem, apparently it has to do with the ulimit for file descriptor for the slapd daemon. That helped for finding a solution.
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AlexD

You have an out of memory error and your process is being killed by the kernel. The process allocated a mere 334664KB of RSS, you need to increase your memory limits.

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