[Docker] Skip actions if the host distro does not match the image distro

[alexzhc]

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Piraeus kernel-module-injector uses entry.sh from drbd/docker repo.

As discussed with @WanzenBug, a good way to have Piraeus support a Kubernetes cluster with mixed Linux distros, is to have multiple kernel-module-injector initContainers of piraeus-node pods, as demonstrated in drbd-adapter.

Therefore, drbd containers must be able to skip actions (and exit 0) when the host distro does not match the image distro.

Signed-off-by: alexzhc [email protected]

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[rck]

having this MR handled here is fine, reopening

[rck]

I probably want to have that in a function and maybe do the shell stuff slightly different, but all in all the direction this is going should be fine. I will discuss it with Moritz next week.

[rck]

one thing we need to keep in mind, I simply don't know that from top of my head: can we assume that $HOSTRELEASE is bind mounted? maybe all the relevant users (e.g., operator) do that, but so far that is only required when we want to fetch packages from LINBIT repos per hash. A very obscure use case, but the only one so far that would need $HOSTRELEASE. no blocker, and something we could handle with some more shell checks, just something to consider

[alexzhc]

If /etc/host-release is not bind mounted, host_dist will be empty. [ -z $host_dist ] also skips the actions.

yes, a function verify_dist should be better. Let me try emulate the style in other functions.

[rck]

JFI, this is on hold till the proposed function is provided

[alexzhc]

@rck, I've pushed the function host_dist_matches_image_dist()

[alexzhc]

adjusted host_dist_matches_image_dist per above review

[rck]

hi @alexzhc ,

I did some cleanups (trainling white spaces, spelling), and I think I might want to have that code a bit further down, after the check if the drbd module is already loaded. Guess there is no need to do all the LB_SKIP magic if the module is already there. Would the below version work for you?

diff --git a/docker/entry.sh b/docker/entry.sh
index c78e959ba..e3c478d82 100644
--- a/docker/entry.sh
+++ b/docker/entry.sh
@@ -29,6 +29,23 @@ map_dist() {
        return 0
 }

+host_dist_matches_image_dist() {
+       host_dist="$( map_dist | cut -d'.' -f1 )"
+       if [[ -z "$host_dist" ]] ; then
+               debug "Cannot get host distro!"
+               return 1
+       fi
+
+       image_dist="$( lbdisttool.py -l | cut -d'.' -f1 )"
+       if [[ "$host_dist" == "$image_dist" ]]; then
+               debug "The host distro matches image distro!"
+               return 0
+       else
+               debug "The host distro does not match image distro"
+               return 1
+       fi
+}
+
 print_drbd_version() {
        echo
        echo "DRBD version loaded:"
@@ -234,6 +251,16 @@ if grep -q '^drbd ' /proc/modules; then
        exit 0
 fi

+# LB_SKIP
+# allows skipping if the linux distro of the host does not match that of this image
+# Allow "exit 0", so that when used as an initContainer in Kubernetes,
+# next initContainer with a different distro will be tried
+if [[ $LB_SKIP == yes ]]; then
+       host_dist_matches_image_dist || exit 0
+elif [[ $LB_SKIP == no ]]; then
+       host_dist_matches_image_dist || exit 1
+fi
+
 pkgdir=/tmp/pkg
 kodir=/tmp/ko
 rm -rf "$pkgdir" "$kodir"

[alexzhc]

hi, @rck. The idea is make it possible to exit 0 when both of the below conditions are met

• the kernel module is not loaded
• the image distro does not match the host distro

so that the kubernetes may skip the current initContainer and start the next intiContainer.

If exit 1 under such conditions, the kubernetes will stop the pod at the failed initContainer and never start the next.

[rck]

@alexzhc I get that, there is no set -e, it would just try to load the deps but not fail. The idea was to not run any code (besides depencency loading) if the DRBD module is already there, not even the dirsto-detection. Anyways, one can argue that LB_SKIP has the semantic to not run any further code if host and container don't match, fair enough. Moved that part to the top again. OK?

diff --git a/docker/entry.sh b/docker/entry.sh
index c78e959ba..c5d022676 100644
--- a/docker/entry.sh
+++ b/docker/entry.sh
@@ -29,6 +29,23 @@ map_dist() {
        return 0
 }

+host_dist_matches_image_dist() {
+       host_dist="$( map_dist | cut -d'.' -f1 )"
+       if [[ -z "$host_dist" ]] ; then
+               debug "Cannot get host distro!"
+               return 1
+       fi
+
+       image_dist="$( lbdisttool.py -l | cut -d'.' -f1 )"
+       if [[ "$host_dist" == "$image_dist" ]]; then
+               debug "The host distro matches image distro!"
+               return 0
+       else
+               debug "The host distro does not match image distro"
+               return 1
+       fi
+}
+
 print_drbd_version() {
        echo
        echo "DRBD version loaded:"
@@ -221,6 +238,16 @@ modprobe_deps() {
 }

 ### main
+# LB_SKIP
+# allows skipping (or failing) if the linux distro of the host does not match that of this image
+# Allow "exit 0", so that when used as an initContainer in Kubernetes,
+# next initContainer with a different distro will be tried
+if [[ $LB_SKIP == yes ]]; then
+       host_dist_matches_image_dist || exit 0
+elif [[ $LB_SKIP == no ]]; then
+       host_dist_matches_image_dist || exit 1
+fi
+
 modprobe_deps
 [[ $LB_HOW == "$HOW_DEPSONLY" ]] && { debug "dependencies loading only, exiting now"; exit 0; }

[alexzhc]

Thanks, I have update the PR per your revision.

[rck]

thanks, a 'yes' would have been enough. For DRBD we don't do merges, we always rebase, but anyways, I will queue that in internally, it should merged and pushed soon. after that I will close this ticket

[rck]

This is now on the drbd-9.1 branch as 973ba0c7083bea597c98460a95cd99962da2545b and also got forward merged to master