PollyScript is a JavaScript resilience and transient-fault-handling library that allows developers to express policies such as Retry, Circuit Breaker, Timeout, Bulkhead Isolation, and Fallback in a fluent and thread-safe manner. PollyScript is a port of the Polly library from .NET.
$ npm install @the-pat/pollyscript
PollyScript aims to offer the same resilience policies as Polly.
| Policy | Premise | Aka | How does the policy mitigate? |
|---|---|---|---|
| Retry (policy family) (quickstart ; deep) |
Many faults are transient and may self-correct after a short delay. | "Maybe it's just a blip" | Allows configuring automatic retries. |
| Circuit-breaker (policy family) (quickstart ; deep) |
When a system is seriously struggling, failing fast is better than making users/callers wait. Protecting a faulting system from overload can help it recover. |
"Stop doing it if it hurts" "Give that system a break" |
Breaks the circuit (blocks executions) for a period, when faults exceed some pre-configured threshold. |
| Timeout (quickstart ; deep) |
Beyond a certain wait, a success result is unlikely. | "Don't wait forever" | Guarantees the caller won't have to wait beyond the timeout. |
| Bulkhead Isolation (quickstart ; deep) |
When a process faults, multiple failing calls backing up can easily swamp resource (eg threads/CPU) in a host. A faulting downstream system can also cause 'backed-up' failing calls upstream. Both risk a faulting process bringing down a wider system. |
"One fault shouldn't sink the whole ship" | Constrains the governed actions to a fixed-size resource pool, isolating their potential to affect others. |
| Cache (quickstart ; deep) |
Some proportion of requests may be similar. | "You've asked that one before" | Provides a response from cache if known. Stores responses automatically in cache, when first retrieved. |
| Fallback (quickstart ; deep) |
Things will still fail - plan what you will do when that happens. | "Degrade gracefully" | Defines an alternative value to be returned (or action to be executed) on failure. |
| PolicyWrap (quickstart ; deep) |
Different faults require different strategies; resilience means using a combination. | "Defence in depth" | Allows any of the above policies to be combined flexibly. |