Design Decision: Near-term target for node HA

Background / Context

Designing for high availability is a complex task which can only be delivered over an operationally-significant timeline. It is therefore important to determine the target state in the near term as a precursor to longer term outcomes.

Options Analysis

1. No HA

Advantages

  1. Reduces developer distractions.

Disadvantages

  1. No backstop if we miss our targets for fuller HA.
  2. No answer at all for simple DR modes.

2. Hot-cold (see HA design doc)

Advantages

  1. Flushes out lots of basic deployment issues that will be of benefit later.
  2. If stuff slips we at least have a backstop position with hot-cold.
  3. For now, the only DR story we have is essentially a continuation of this mode
  4. The intent of decisions such as using a loadbalancer is to minimise code changes

Disadvantages

  1. Distracts from the work for more complete forms of HA.
  2. Involves creating a few components that are not much use later, for instance the mutual exclusion lock.

Recommendation and justification

Proceed with Option 2: Hot-cold.