Docker network bridge not working on Yocto Hardknott

Docker network bridge not working on Yocto Hardknott

[Morgan Baugh]

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Hi All,

I have built a Yocto Hardknott image for the i.MX8 according to the 
following Variscite tutorial: Yocto Build Release | Variscite Wiki 
<https://variwiki.com/index.php?title=Yocto_Build_Release&release=mx8-yocto-hardknott-5.10.72_2.2.1-v1.1>

Then, I added Docker by setting the following in local.conf:
IMAGE_INSTALL_append = " docker"
DISTRO_FEATURES_append = " virtualization"

The image builds fine, boots, and runs Docker (which takes a few minutes 
to start), however, the containers fail to connect to the docker0 
bridge. For example, an Nginx container will not emit the expected 
boilerplate HTML via curl:

root@imx8qm-var-som:~# docker run -p 80:80 -d nginx
root@imx8qm-var-som:~# curl localhost
root@imx8qm-var-som:~# curl: (56) Recv failure: Connection reset by peer

This problem can be temporarily overcome by brctl:

root@imx8qm-var-som:~# brctl addif docker0 $(ifconfig | grep veth | cut 
-c 1-11)
root@imx8qm-var-som:~# curl localhost
html stuff that won’t render properly on the forum…

Specifically, Docker is not adding the veth interface to the docker0 
bridge upon container creation/restart. I have tried modifying the Yocto 
build to replace NetworkManager with connman or nothing at all, but this 
doesn’t make a difference. In fact, when NetworkManager is running, 
“nmcli device status” shows docker0 as “connected (externally)”, which, 
to my knowledge, means that something other than NetworkManager is 
responsible for it.

I have repeated the test on a Dunfell version of the Variscite Yocto 
build, as well as a non-Variscite build of Yocto Hardknott for the 
Raspberry Pi 4, and Docker’s network bridge functions properly in both 
cases. However, swapping the meta-virtualization layer (which contains 
Docker itself among other things), meta-openembedded, or the Linux 
kernel from these into the Variscite Hardknott build doesn’t solve the 
problem. I had once considered the possibility that containerd was at 
fault, however, that is part of meta-virtualization, and would have been 
fixed by swapping that layer if it was the problem.

To recap, the problem appears to be specific to Variscite + Yocto 
Hardknott + Docker, and consists of a failure to automatically add the 
veth to docker0. Running the container with host networking does work, 
but is not suitable for my application. Any help would be greatly 
appreciated!

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