release-21.1: backport a doc fix

[knz]

Backporting 1/1 commit from #78255

Informs #84024

cc @cockroachdb/release

Release justification: doc-only change

[blathers-crl]

Thanks for opening a backport.

Please check the backport criteria before merging:

• Patches should only be created for serious issues or test-only changes.
• Patches should not break backwards-compatibility.
• Patches should change as little code as possible.
• Patches should not change on-disk formats or node communication protocols.
• Patches should not add new functionality.
• Patches must not add, edit, or otherwise modify cluster versions; or add version gates.

If some of the basic criteria cannot be satisfied, ensure that the exceptional criteria are satisfied within.

• There is a high priority need for the functionality that cannot wait until the next release and is difficult to address in another way.
• The new functionality is additive-only and only runs for clusters which have specifically “opted in” to it (e.g. by a cluster setting).
• New code is protected by a conditional check that is trivial to verify and ensures that it only runs for opt-in clusters.
• The PM and TL on the team that owns the changed code have signed off that the change obeys the above rules.

Add a brief release justification to the body of your PR to justify this backport.

Some other things to consider:

• What did we do to ensure that a user that doesn’t know & care about this backport, has no idea that it happened?
• Will this work in a cluster of mixed patch versions? Did we test that?
• If a user upgrades a patch version, uses this feature, and then downgrades, what happens?

[cockroach-teamcity]

This change is 

[knz]

@rickystewart I see a skew in CI for this PR, between one of our dependencies and the go runtime version included inside the acceptance test container image:

(NB: this test runs under acceptance, so using the acceptance image and not the CI native toolchain)

How can we resolve this?

[rickystewart]

The actual problem here is that we build the Dockerfile in an ad-hoc way during the test execution instead of building the image once and pulling the appropriate version at test time. This has bitten us before and will undoubtedly bite us again.

Regarding how to fix, it looks like the Dockerfile installs Go via the golang debian package. Instead of doing that we should download the appropriate prebuilt x86 archive and install it.

[knz]

we should download the appropriate prebuilt x86 archive and install it.

ok. I know how to edit a dockerfile. What would be a good link to use?

[rickystewart]

we should download the appropriate prebuilt x86 archive and install it.

ok. I know how to edit a dockerfile. What would be a good link to use?

Elsewhere in release-21.1 we are using Golang 1.15.14, so we probably should be using the same here. Copied from bootstrap-debian.sh:

# Install Go.
trap 'rm -f /tmp/go.tgz' EXIT
curl -fsSL https://dl.google.com/go/go1.15.14.linux-amd64.tar.gz > /tmp/go.tgz
sha256sum -c - <<EOF
6f5410c113b803f437d7a1ee6f8f124100e536cc7361920f7e640fedf7add72d /tmp/go.tgz
EOF
sudo tar -C /usr/local -zxf /tmp/go.tgz && rm /tmp/go.tgz

[knz]

After investigation, the issue we're having here is that the go source code used as input to the test is too new for the go compiler used in the docker image: it uses os.ReadFile, which was only introduced in go 1.16.

I'll make the necessary change.

[knz]

Done, RFAL

[knz]

I'm going to go by the green CI and the previous review approval and merge this.