Ubuntu-based Logstash Keystore Permissions Issues

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Background: I'm working in an Ubuntu 20.04 environment setting up Logstash servers to ship metrics to my Elastic cluster. With my relatively basic configuration, I'm able to have a Filebeat process send logs to a Loadbalancer, which then spreads them across my Logstash servers and up to Elastic. This process works. I'd like to be able to use the Logstash Keystore to prevent having to pass sensitive variables to my logstash.yml file in plain text. In my environment, I'm able to follow the Elastic documentation to setup a password-protected keystore in the default location, add keys to it, and successfully list out those keys.

Problems: While the Logstash servers successfully run without the keystore, the moment I add them and try to watch the logfile on startup, the process never starts. It seems to continue attempting restart without ever logging to the logstash-plain.log. When trying to run the process in the foreground with this configuration, the error I received was the rather-unhelpful:

Found a file at /etc/logstash/logstash.keystore, 
but it is not a valid Logstash keystore

Troubleshooting Done: After trying some steps found in other issues, such as replacing the /etc/sysconfig/logstash creation with simply adding the password to /etc/default/logstash, the errors were a little more helpful, stating that the file permissions or password were incorrect. The logstash-keystore process itself was capable of creating and listing keys, so the password was correct, and the keystore itself was set to 0644. I tried multiple permissions configurations and was still unable to get Logstash to run as a process or in the foreground.

I'm still under the impression it's a permissions issue, but I don't know how to resolve it. Logstash runs as the logstash user, which should be able to read the keystore file since its 0644 and housed in the same dir as logstash.yml.

Has anyone experienced something similar with Logstash & Ubuntu, or in a similar environment? If so, how did you manage to get past it? I'm open to ideas and would love to get this working.

logstash-configuration elastic-stack logstash elasticsearch permissions
1 Answers

Try running logstash-keystore as the logstash user:

sudo -u logstash /usr/share/logstash/bin/logstash-keystore \
  --path.settings /etc/logstash list

[Aside from the usual caveats about secret obfuscation of this kind, it's worth making explicit that the docs expect logstash-keystore to be run as root, not as logstash. So after you're done troubleshooting, especially if you create a keystore owned by logstash, make sure it ultimately has permissions that are sufficiently restrictive]

Alternatively, you could run some other command as the logstash user. To validate the permission hypothesis, you just need to read the file as user logstash:

sudo -u logstash file /etc/logstash/logstash.keystore
sudo -u logstash md5sum /etc/logstash/logstash.keystore
su logstash -c 'cat /etc/logstash/logstash.keystore > /dev/null'
# and so on

If, as you suspect, there is a permissions problem, and the read test fails, assemble the necessary data with these commands:

ls -dla /etc/logstash/{,logstash.keystore}
groups logstash

By this point you should know:

  • what groups logstash is in
  • what groups are able to open /etc/logstash
  • what groups are able to read /etc/logstash/logstash.keystore

And you already said the keystore's mode is 644. In all likelihood, logstash will be a member of the logstash group only, and /etc/logstash will be world readable. So the TL;DR version of this advice might be:

# set group on the keystore to `logstash`
chgrp logstash /etc/logstash/logstash.keystore
# ensure the keystore is group readable
chmod g+r /etc/logstash/logstash.keystore

If it wasn't permissions, you could try recreating the store without a password. If it then works, you'll want to be really careful about how you handle the password environment variable, and go over the docs with a fine-tooth comb.

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