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* NOTE: the fnproject/dind release will need recutting and the
top-level Dockerfile updated to refer to it for this to be
complete.
In many k8s environments the host docker uses an overlay network
which'll take bytes away from the effective MTU of outer
containers; eg, vxlan needs 50 bytes, often leaving a 1450 MTU
on the container running dind and fn-api.
In such an arrangement, packets exceeding the smaller MTU may be
invisibly dropped as they travel across the dind's docker0
bridge. This mostly surfaces as a failure of functions to be able
to reliably talk to external services. (Note, the failure may be
intermittent depending on the profile of the resulting TCP
communication.)
A robust fix for this is to intercept the startup of the dind
dockerd and ensure that /etc/docker/daemon.json (currently
absent) contains the following setting:
{
"mtu": 1450
}
(or whatever the MTU on the external interface may be). This
should be autosized so the container works in a variety of
deployments.
The problem does not arise when using an embedded
/var/run/docker.sock - or when running with dind on a host that
can supply 1500-byte MTUs to containers on the 'host' docker.
708 B
708 B
Docker-in-Docker Base Image
This is the base image for all docker-in-docker images.
The difference between this and the official docker images are that this will choose the best
filesystem automatically. The official ones use vfs (bad) by default unless you pass in a flag.
It will also attempt to mirror the default external interface's MTU to the dind network; this addresses a problem with running dind-based images on a kubernetes cluster with an overlay network that takes a chunk out of pods' MTUs.
Usage
Just use this as your base image and use CMD for your program, NOT ENTRYPOINT. This will handle the rest.
FROM fnproject/dind
# OTHER STUFF
CMD ["./myproggie"]