Variable substitution in a configuration file - kubernetes

Question

Variable substitution in Gitlab only seem to work inside the gitlab-ci.yml file.
However I have a configuration file (k8s secret) where I would like to set different values depending if I'm in a staging or a production environment.
apiVersion: v1
kind: Secret
metadata:
name: tls-config
namespace: myNamespace
type: kubernetes.io/tls
data:
tls.crt: |
${TLS_CRT}
tls.key: |
${TLS_KEY}
Where TLS_CRT & TLS_KEY would be variables defined in /settings/ci_cd/variables.
How should one handle variable substitution in this case?

Answer 1

You could use an editor like sed
For example, if you had the file like:
data:
tls.crt: |
#TLS_CRT#
tls.key: |
#TLS_KEY#
You could use sed like this as part of your GitLab job to replace its contents:
myjob:
script:
- sed -i "s|#TLS_CRT#|${TLS_CRT}|" ./path/to/file
- sed -i "s|#TLS_KEY#|${TLS_KEY}|" ./path/to/file
Then the file contents will be something like this:
data:
tls.crt: |
MIIC2DCCAcCgAwIBAgIBATANBgkqh ...
tls.key: |
MIIEpgIBAAKCAQEA7yn3bRHQ5FHMQ ...
Using the pattern #word# is not totally necessary. However, it does make using the sed easier, as it avoids needing to escape the literal ${} characters in the shell command.
As a short explanation of the sed command used here:
# v shorthand for --in-place; edits the file directly
sed -i "s|FIRST_ARGUMENT|SECOND_ARGUMENT|" ./path/to/file
# ^ replace this ^ with this ^ in this file
Fore more info, see here: https://unix.stackexchange.com/a/112024/453397