Detail Calico BGP route reflector requirements

[Vlaaaaaaad]

As per Lance Robson's( aka @lwr20 ) message in Slack, above 50-100 nodes Calico recommends usage of BGP route reflectors:

Clearly I'm not impartial here, but I can tell you that we test Calico to 5K nodes.
We recommend BGP route reflectors once you go above ~50-100 nodes (we test up to 100 nodes without RRs). The reason for RRs is that by default calico sets up BGP connections in a full mesh - clearly the number of connections will scale as the number of nodes squared. With RRs, the number of BGP connections scales linearly with nodes - but then you have to manage the RRs too.
The next version of Calico (v3.3 - code is in master already, but not heavily tested yet) will bring a feature to make RRs much easier to deploy - just annotate a few nodes and they become RRs.

Adding this detail to documentation as I recently got a cluster with such issues.

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[justinsb]

/approve
/lgtm

Thanks @Vlaaaaaaad

Seems like a fairly big limitation of calico :-(

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[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: justinsb, Vlaaaaaaad

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[Vlaaaaaaad]

This is a docs change and has 0 impact. Might be a flaky test? Either way, rerunning.

/test pull-kops-e2e-kubernetes-aws

[k8s-ci-robot]

@Vlaaaaaaad: Cannot trigger testing until a trusted user reviews the PR and leaves an /ok-to-test message.

In response to this:

This is a docs change and has 0 impact. Might be a flaky test? Either way, rerunning.

/test pull-kops-e2e-kubernetes-aws

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[justinsb]

Yes, it's a boo-boo where the CNCF test account lost quota in a few regions: kubernetes/test-infra#10043

I'll make sure we get this merged once e.g. kubernetes/test-infra#10116 lands

[justinsb]

/retest