Setup Semian Configuration Validation

[abishanan-shopify]

Addressing this issue: #633

Changes

Created ConfigurationValidator class that handles all validations and constraints for the following Semian config values:

• name: Must be string / symbol and cannot be a duplicate Semian name of one that exists in Semian.resources
• :circuit_breaker & :bulkhead: Cannot both be disabled
• :tickets & :quota: If bulkhead, can only have :tickets or :quota, cannot be both
  • :tickets: Must be between 0 and Semian::MAX_TICKETS, inclusive
  • :quota: Must be a ratio between 0 and 1, inclusive
• :success_threshold, :error_threshold & :error_timeout: If circuit breaker, validate that these required params exist.
• :success_threshold & :error_threshold: If circuit breaker, validate that they are positive numbers
• :error_timeout, :error_threshold_timeout, :half_open_resource_timeout, :lumping_interval: If circuit breaker and exists, validate that they are non-negative.

We have also added constraints to the timeout values to ensure that Semians don't end up in weird scenarios (never opens, closes, never half-opens, etc.):

• lumping_interval * (error_threshold - 1) <= error_threshold_timeout

We also added a new flag - force_config_validation to pass as an argument to Semian to force configuration validation at runtime if desired (otherwise it will be logged verbosely in I/O)

Finally, we added test cases to address each of the above constraints, and modified non-validation related test cases to conform to ConfigurationValidator class.

Rationale

We are looking to add validations to configuration options on Semians, to ensure that invalid or otherwise impossible Semian configuration are not created (result in an Exception raised) and do not persist in production. This will help alleviate any cases of incidents or investigations where Semians do not open due to impossible conditions.

Why are some validations required and others are not?

This is to avoid regression in our previous validation logic -- we want to make sure that we don't unexpectedly crash developers' Semians, but we don't allow things that we have previously disallowed.

This includes:

• Requiring success_threshold, error_threshold, and error_timeout to be required in circuit breakers
• Requiring either tickets or quota to be required in bulkheads
• Making sure tickets are within bounds (0, MAX_TICKETS] (tickets != MAX_TICKETS was not previously enforced so we use flag instead)
• Making sure quota is within bounds (0, 1] (quota != 1 was not previously enforced so we use the flag instead)

[AbdulRahmanAlHamali]

Note: CI on this PR (and others) have been failing because example.com has been acting funkily. We switched all usages to shopify.com instead.

(Ideally we would put these changes in a separate PR, but they are sufficiently trivial)

[iandelahorne]

edit: my previous comment was in error, but this should likely be a minor version bump when we release it

[iandelahorne]

Looks good, excited to see this in production later