Make amd64 calico/bird image useful for testing as well as for holding BIRD binaries

[nelljerram]

Currently (prior to this PR), the calico/bird container image is used only as an intermediate step towards the production of a deliverable calico/node container image. Specifically, we use the calico/bird container image just as a way to wrap and publish the various BIRD binaries (on multiple architectures):

• bird
• bird6
• birdcl
• birdcl6

Then the calico/node build process pulls that image and copies the BIRD binaries out of it to the right place in the calico/node image.

Now - especially with the recent dual ToR work - we need something to model a router that is not a Calico node, and it's convenient to use BIRD for that too, as we're familiar with its config and operation. I have built a container image for that purpose from a different Dockerfile than calico/bird, and published it as "neiljerram/birdy", but:

• I haven't yet finalised the coding and process for that image
• I think it's confusing for our BIRD repo to generate two container images for different purposes
• I think we can add the "birdy" testing role into the existing calico/bird image without jeopardising the current uses of the calico/bird image.

So, the last bullet is what this PR does. For simplicity, for amd64 only, because we only need to test on amd64.

• BIRD binaries are copied into the image at the same location (/) as before.
• Then, to make the image runnable and useful for testing:
  • Base is changed from scratch to alpine.
  • BIRD binaries are linked to standard locations in PATH.
  • Required runtime and config directories are created.
  • Basic config is added in.
  • Added a wrapper script that discovers the container's IPv4 and runs BIRD and BIRD6 with that IPv4 as router ID.

I have tested successfully that:

• This repo's image build and publishing still works: https://semaphoreci.com/calico/bird/branches/container-image-for-tor/builds/2.
• Node CI still passes when node is updated to use this new BIRD image build: https://github.com/projectcalico/node/pull/415.

[nelljerram]

@song-jiang

Just wondering once PR is merged, should we switch node k8st to use new image?

Yes I will make sure to do that. I believe there are 2 cases:

• The IPv6 service advertisement testing. The image change will be in the PR that I will post shortly.
• The dual ToR testing in node-private. I will post a separate PR for that.