|2018-04-22||MTU issues with Docker||[linux netcat]||Troubles with Drone on Kubernetes||false|
Currently, I am trying out drone to automate building of docker images for my kubernetes cluster.
I have a Docker-in-Docker (DIND) setup in Kubernetes to enable building docker containers in drone. Yes, those are a lot of Docker layers! Kubernetes, then drone, the whatever Docker containers drone is building ... but it works! At least, now it does. Before, I noticed that I did not have network connectivity inside the build containers. DNS was working, but pinging did not. The
.drone.yml file looks like this:
pipeline: build: image: docker:17.12.1 volumes: - /var/run/docker.sock:/var/run/docker.sock commands: - apk update - apk add make git - make
I did not want to use DIND containers for every build step, but drone should use a single DIND container for all builds to use. This was done like this in the kubernetes deployment:
spec: containers: - image: docker:17.12.1-dind name: dind ports: - containerPort: 2375 protocol: TCP securityContext: privileged: true - image: drone/agent:0.8 name: drone-agent args: - agent env: - name: DRONE_SECRET value: [...] - name: DRONE_SERVER value: [...] - name: DOCKER_HOST value: tcp://localhost:2375
Exept, that did not work, showing the network connectivity issues mentioned above.
In the end, I tracked it down to an MTU issue, also mentioned here. The fix is a bit ugly, because the DIND container does not expose a straight way to set the MTU. The simplest solution (after looking into the DIND build environment) I found was to set the startup arguments for the DIND container explicitly in the kubernetes deployment:
- image: docker:17.12.1-dind name: dind + command: + - dockerd-entrypoint.sh + - dockerd + - --host=unix:///var/run/docker.sock + - --host=tcp://localhost:2375 + - --mtu=1400 + - --storage-driver=vfs ports: - containerPort: 2375 protocol: TCP securityContext: privileged: true
With these changes, network connectivity for the build containers is restored, and drone can build docker containers without issues.
Hopefully, in one of my next posts I might describe how this blog is then automatically built using drone ;)