Gerrit replica on Kubernetes

Gerrit is a web-based code review tool, which acts as a Git server. On large setups Gerrit servers can see a sizable amount of traffic from git operations performed by developers and build servers. The major part of requests are read-only requests (e.g. by git fetch operations). To take some load of the Gerrit server, Gerrit replicas can be deployed to serve read-only requests.

This helm chart provides a Gerrit replica setup that can be deployed on Kubernetes. The Gerrit replica is capable of receiving replicated git repositories from a Gerrit. The Gerrit replica can then serve authenticated read-only requests.

Prerequisites

• Helm (>= version 3.0)

  (Check out this guide how to install and use helm.)

• Access to a provisioner for persistent volumes with Read Write Many (RWM)- capability.

  A list of applicaple volume types can be found here. This project was developed using the NFS-server-provisioner helm chart, a NFS-provisioner deployed in the Kubernetes cluster itself. Refer to this guide of how to deploy it in context of this project.

• A domain name that is configured to point to the IP address of the node running the Ingress controller on the kubernetes cluster (as described here).

• (Optional: Required, if SSL is configured) A Java keystore to be used by Gerrit.

Installing the Chart

To install the chart with the release name gerrit-replica, execute:

cd $(git rev-parse --show-toplevel)/helm-charts
helm install \
  gerrit-replica \  # release name
  ./gerrit-replica \  # path to chart
  -f <path-to-custom-values>.yaml

The command deploys the Gerrit replica on the current Kubernetes cluster. The configuration section lists the parameters that can be configured during installation.

The Gerrit replica requires the replicated All-Projects.git- and All-Users.git- repositories to be present in the /var/gerrit/git-directory. The gerrit-init- InitContainer will wait for this being the case. A way to do this is to access the Gerrit replica pod and to clone the repositories from the primary Gerrit (Make sure that you have the correct access rights do so.):

kubectl exec -it <gerrit-replica-pod> -c gerrit-init ash
gerrit@<gerrit-replica-pod>:/var/tools$ cd /var/gerrit/git
gerrit@<gerrit-replica-pod>:/var/gerrit/git$ git clone "http://gerrit.com/All-Projects" --mirror
Cloning into bare repository 'All-Projects.git'...
gerrit@<gerrit-replica-pod>:/var/gerrit/git$ git clone "http://gerrit.com/All-Users" --mirror
Cloning into bare repository 'All-Users.git'...

Configuration

The following sections list the configurable values in values.yaml. To configure a Gerrit replica setup, make a copy of the values.yaml-file and change the parameters as needed. The configuration can be applied by installing the chart as described above.

In addition, single options can be set without creating a custom values.yaml:

cd $(git rev-parse --show-toplevel)/helm-charts
helm install \
  gerrit-replica \  # release name
  ./gerrit-replica \  # path to chart
  --set=gitRepositoryStorage.size=100Gi,gitBackend.replicas=2

Container images

Storage classes

For information of how a StorageClass is configured in Kubernetes, read the official Documentation.

Workaround for NFS

Kubernetes will not be able to adapt the ownership of the files within NFS volumes. Thus, a workaround exists that will add init-containers and jobs to adapt file ownership. Also the ID-domain will be configured to ensure correct ID-mapping.

Network policies

The NetworkPolicies provided here are quite strict and do not account for all possible scenarios. Thus, custom NetworkPolicies have to be added, e.g. for connecting to a database. On the other hand some defaults may be not restrictive enough. By default, the ingress traffic of the git-backend pod is not restricted. Thus, every source (with the right credentials) could push to the git-backend. To add an additional layer of security, the ingress rule could be defined more finegrained. The chart provides the possibility to define custom rules for ingress- traffic of the git-backend pod under gitBackend.networkPolicy.ingress. Depending on the scenario, there are different ways to restrict the incoming connections.

If the replicator (e.g. Gerrit) is running in a pod on the same cluster, a podSelector (and namespaceSelector, if the pod is running in a different namespace) can be used to whitelist the traffic:

gitBackend:
  networkPolicy:
    ingress:
    - from:
      - podSelector:
          matchLabels:
            app: gerrit

If the replicator is outside the cluster, the IP of the replicator can also be whitelisted, e.g.:

gitBackend:
  networkPolicy:
    ingress:
    - from:
      - ipBlock:
          cidr: xxx.xxx.0.0/16

The same principle also applies to other use cases, e.g. connecting to a database. For more information about the NetworkPolicy resource refer to the Kubernetes documentation.

Storage for Git repositories

If the git repositories should be persisted even if the chart is deleted and in a way that the volume containing them can be mounted by the reinstalled chart, the PVC claiming the volume has to be created independently of the chart. To use the external PVC, set gitRepositoryStorage.externalPVC.enabled to true and give the name of the PVC under gitRepositoryStorage.externalPVC.name.

Storage for Logs

In addition to collecting logs with a log collection tool like Promtail, the logs can also be stored in a persistent volume. This volume has to be a read-write-many volume to be able to be used by multiple pods.

Each pod will create a separate folder for its logs, allowing to trace logs to the respective pods.

Istio

Istio can be used as an alternative to Kubernetes Ingresses to manage the traffic into the cluster and also inside the cluster. This requires istio to be installed beforehand. Some guidance on how to set up istio can be found here. The helm chart expects istio-injection to be enabled in the namespace, in which it will be installed.

In the case istio is used, all configuration for ingresses in the chart will be ignored.

Promtail Sidecar

To collect Gerrit logs, a Promtail sidecar can be deployed into the Gerrit replica pods. This can for example be used together with the gerrit-monitoring project.

Apache-Git-HTTP-Backend (Git-Backend)

Git garbage collection

Gerrit replica

Gerrit config files

The gerrit-replica chart provides a ConfigMap containing the configuration files used by Gerrit, e.g. gerrit.config and a Secret containing sensitive configuration like the secure.config to configure the Gerrit installation in the Gerrit component. The content of the config files can be set in the values.yaml under the keys gerritReplica.etc.config and gerritReplica.etc.secret respectively. The key has to be the filename (eg. gerrit.config) and the file's contents the value. This way an arbitrary number of configuration files can be loaded into the $GERRIT_SITE/etc-directory, e.g. for plugins. All configuration options for Gerrit are described in detail in the official documentation of Gerrit. Some options however have to be set in a specified way for Gerrit to work as intended with the chart:

• gerrit.basePath

  Path to the directory containing the repositories. The chart mounts this directory from a persistent volume to /var/gerrit/git in the container. For Gerrit to find the correct directory, this has to be set to git.

• gerrit.serverId

  In Gerrit-version higher than 2.14 Gerrit needs a server ID, which is used by NoteDB. Gerrit would usually generate a random ID on startup, but since the gerrit.config file is read only, when mounted as a ConfigMap this fails. Thus the server ID has to be set manually!

• gerrit.canonicalWebUrl

  The canonical web URL has to be set to the Ingress host.

• httpd.listenURL

  This has to be set to proxy-http://*:8080/ or proxy-https://*:8080, depending of TLS is enabled in the Ingress or not, otherwise the Jetty servlet will run into an endless redirect loop.

• container.user

  The technical user in the Gerrit replica container is called gerrit. Thus, this value is required to be gerrit.

• container.replica

  Since this chart is meant to install a Gerrit replica, this naturally has to be true.

• container.javaHome

  This has to be set to /usr/lib/jvm/java-8-openjdk-amd64, since this is the path of the Java installation in the container.

• container.javaOptions

  The maximum heap size has to be set. And its value has to be lower than the memory resource limit set for the container (e.g. -Xmx4g). In your calculation allow memory for other components running in the container.

To enable liveness- and readiness probes, the healthcheck plugin will be installed by default. Note, that by configuring to use a packaged or downloaded version of the healthcheck plugin, the configured version will take precedence over the default version. The plugin is by default configured to disable the querychanges and auth healthchecks, since the Gerrit replica does not index changes and a new Gerrit server will not yet necessarily have an user to validate authentication.

The default configuration can be overwritten by adding the healthcheck.config file as a key-value pair to gerritReplica.etc.config as for every other configuration.

Upgrading the Chart

To upgrade an existing installation of the gerrit-replica chart, e.g. to install a newer chart version or to use an updated custom values.yaml-file, execute the following command:

cd $(git rev-parse --show-toplevel)/helm-charts
helm upgrade \
  <release-name> \
  ./gerrit-replica \ # path to chart
  -f <path-to-custom-values>.yaml \

Uninstalling the Chart

To delete the chart from the cluster, use:

helm delete <release-name>