GitLab CI script needs entry in /etc/hosts - docker

Question

I have a GitLab CI docker runner to execute my automated tests when I push. One of my tests requires a custom entry in /etc/hosts. I can't figure out how to get the entry into that file.
Here's basically what my .gitlab-ci.yml file looks like:
before_script:
- cat /etc/hosts # for debugging
- ... # install app dependencies
specs:
script:
- rspec # <- a test in here fails without the /etc/hosts entry
All my tests pass, except for the one that requires that /etc/hosts entry.
Let's say I'm trying to have the hostname myhost.local resolve to the IPv4 address XX.XX.XX.XX...
I tried using extra_hosts on the runner config, but it didn't seem to have any effect (got idea from here):
/etc/gitlab-runner/config.toml:
concurrent = 1
check_interval = 0
[[runners]]
name = "shell"
url = "https://mygitlabinstance.com/"
token = "THETOKEN"
executor = "shell"
[runners.cache]
[[runners]]
name = "docker-ruby-2.5"
url = "https://mygitlabinstance.com/"
token = "THETOKEN"
executor = "docker"
[runners.docker]
tls_verify = false
image = "ruby:2.5"
privileged = false
disable_cache = false
volumes = ["/cache"]
shm_size = 0
extra_hosts = ["myhost.local:XX.XX.XX.XX"]
[runners.cache]
But the test still failed. The cat /etc/hosts shows that it's unchanged:
# Your system has configured 'manage_etc_hosts' as True.
# As a result, if you wish for changes to this file to persist
# then you will need to either
# a.) make changes to the master file in /etc/cloud/templates/hosts.tmpl
# b.) change or remove the value of 'manage_etc_hosts' in
# /etc/cloud/cloud.cfg or cloud-config from user-data
#
127.0.1.1 ip-172-31-2-54.ec2.internal ip-172-31-2-54
127.0.0.1 localhost
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
I figured I could just add the entry myself in a before_script line, but I don't seem to be able to execute anything with root privileges in the container:
before_script:
- echo 'XX.XX.XX.XX myhost.local' >> /etc/hosts
...
But that just fails because the gitlab-runner user doesn't have permissions to write to that file. I tried to use sudo, but gitlab-runner can't do that either (echo 'XX.XX.XX.XX myhost.local' | sudo tee --non-interactive --append /etc/hosts --> sudo: a password is required)
So in summary, how can I get my container to have the host entry I need (or how can I execute a before_script command as root)?

Answer 1

The following statement is incorrect:
"But that just fails because the gitlab-runner user doesn't have permissions to write to that file."
The gitlab-runner is not the user executing your before_script, it is the user that runs the container in which your job is executed.
You are using the ruby:2.5 Docker image as far as I can tell and that does not contain any USER reference in its or its parents Dockerfile.
Try adding a whoami command right before your echo 'XX.XX.XX.XX myhost.local' >> /etc/hosts command to verify you are root.
Update
If gitlab-runner is shown as the result of whoamithe docker-executor is not used and instead a shell-executor has picked up the job.

Answer 2

In your config.toml on your Gitlab CI runner, you can add a setting to the config.toml so you can achieve this without touching /etc/hosts.
[runners.docker]
# ... other settings ...
extra_hosts = ["myhost.local:xx.xx.xx.xx"]
You can read more about the extra_hosts configuration here: https://docs.gitlab.com/runner/configuration/advanced-configuration.html#the-runnersdocker-section