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Use HostNetwork or LoadBalancer for Ingress

  • Status: accepted
  • Deciders: Axel, Cristian, Fredrik, Johan, Olle, Viktor
  • Date: 2021-02-09

Technical Story: Ingress configuration

Context and Problem Statement

Many regulations require traffic to be encrypted over public Internet. Welkin solves this problem via an Ingress Controller and cert-manager. As of February 2021, Welkin comes by default with Ingress-NGINX, but Ambassador is planned as an alternative. The question is, how does traffic arrive at the Ingress Controller?

Decision Drivers

  • We want to obey the Principle of Least Astonishment.
  • We want to cater to hybrid cloud deployments, including bare-metal ones, which might lack support for Kubernetes-controlled load balancer.
  • Some deployments, e.g., Bring-Your-Own VMs, might not allow integration with the underlying load balancer.
  • We want to keep things simple.

Considered Options

Decision Outcome

Chosen options:

  1. Use host network if Kubernetes-controlled load balancer is unavailable or undesired. If necessary, front the worker nodes with a manual or Terraform-controlled load-balancer. This includes:

    • Where load-balancing does not add value, e.g., if a Deployment is planned to have only a single-node or single-worker for the foreseeable future: Point the DNS entry to the worker IP instead.
    • Exoscale currently falls in this category, due to its Kubernetes integration being rather recent.
    • Safespring falls in this category, since it is missing load balancers.
    • If the Infrastructure Provider is missing a storage controller, it might be undesirable to perform integration "just" for load-balancing.

  2. Use Service type LoadBalancer when available. This includes: AWS, Azure, GCP and CityCloud.

Additional considerations: This means that, generally, it will not be possible to set up the correct DNS entries until after we apply Welkin Apps. There is a risk for "the Internet" -- Let's Encrypt specifically -- to perform DNS lookups too soon and cause negative DNS caches with a long lifetime. Therefore, placeholder IP addresses must be used, e.g.:

*.$BASE_DOMAIN     60s A 203.0.113.123
*.ops.$BASE_DOMAIN 60s A 203.0.113.123

203.0.113.123 is in TEST-NET-3 and okay to use as placeholder. This approach is inspired by kops and should not feel astonishing.

Positive Consequences

  • We make the best of each Infrastructure Provider.
  • Obeys principle of least astonishment.
  • We do not add a load balancer "just because".

Negative Consequences

  • Complexity is a bit increased, however, this feels like essential complexity.