CI: no logging by default

Jenkinsfile

@@ -7,6 +7,27 @@ pipeline {
     }
 
     environment {
+        /*
+          Change this into "true" to enable capturing the journalctl
+          output of the build host and each VM, either by editing the
+          Jenkinsfile in a PR or by logging into Jenkins and editing
+          the pipeline before running it again.
+        */
+        LOGGING_JOURNALCTL = "false"
+
+        /*
+          Delay in seconds between dumping system statistics.
+        */
+        LOGGING_SAMPLING_DELAY = "60"
+
+        /*
+          Pod names in the kube-system namespace for which
+          log output is to be captured. Empty by default,
+          valid values:
+          etcd kube-apiserver kube-controller-manager kube-scheduler
+        */
+        LOGGING_PODS = ""
+
         /*
           For each major Kubernetes release we need one version of Clear Linux
           which had that release. Installing different Kubernetes releases
@@ -360,8 +381,8 @@ void TestInVM(deviceMode, deploymentMode, distro, distroVersion, kubernetesVersi
         */
         sh " \
            mkdir -p build/reports && \
-           sudo journalctl -f & \
-           ( set +x; while true; do sleep 30; top -b -n 1 -w 120 | head -n 20; df -h; done ) & \
+           if ${env.LOGGING_JOURNALCTL}; then sudo journalctl -f; fi & \
+           ( set +x; while true; do sleep ${env.LOGGING_SAMPLING_DELAY}; top -b -n 1 -w 120 | head -n 20; df -h; done ) & \
            docker run --rm \
                   --privileged=true \
                   -e CLUSTER=clear \
@@ -384,16 +405,16 @@ void TestInVM(deviceMode, deploymentMode, distro, distroVersion, kubernetesVersi
                            swupd bundle-add openssh-server && \
                            make start && cd ${env.PMEM_PATH} && \
                            _work/clear/ssh.0 kubectl get pods --all-namespaces -o wide && \
-                           for pod in etcd kube-apiserver kube-controller-manager kube-scheduler; do \
+                           for pod in ${env.LOGGING_PODS}; do \
                                _work/clear/ssh.0 kubectl logs -f -n kube-system \$pod-pmem-csi-clear-master | sed -e \"s/^/\$pod: /\" & \
                            done && \
                            _work/clear/ssh.0 tar -C / -cf - usr/bin/kubectl | tar -C /usr/local/bin --strip-components=2 -xf - && \
                            for ssh in \$(ls _work/clear/ssh.[0-9]); do \
                                hostname=\$(\$ssh hostname) && \
                                ( set +x; \
-                                 while true; do \$ssh journalctl -f; done & \
+                                 if ${env.LOGGING_JOURNALCTL}; then while true; do \$ssh journalctl -f; done; fi & \
                                  while true; do \
-                                     sleep 30; \
+                                     sleep ${env.LOGGING_SAMPLING_DELAY}; \
                                      \$ssh top -b -n 1 -w 120 2>&1 | head -n 20; \
                                  done ) | sed -e \"s/^/\$hostname: /\" & \
                            done && \