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Brown Out Policy

The brownout policy allows performing scheduled downtime on your API. This can be useful for helping notify clients of an impending deprecation or for scheduling maintenance.

This policy uses cron schedules to check if a request should experience a brownout or not. When a request falls into a scheduled brownout an error response will be return. The error response can be customized by setting the problem properties.

For more information using brownouts to alert clients on impending API changes/deprecations see our blog post How to version an API

Configuration

The configuration shows how to configure the policy in the 'policies.json' document.


config/policies.json
{
  "name": "my-brownout-inbound-policy",
  "policyType": "brownout-inbound",
  "handler": {
    "export": "BrownoutInboundPolicy",
    "module": "$import(@zuplo/runtime)",
    "options": {
      "cronSchedule": "* 2 * * *",
      "problem": {
        "type": "https://example.com/problems/deprecation-announcement",
        "title": "Deprecation Test",
        "detail": "This is a temporary brownout every day between 02:00-03:00 to alert of an upcoming deprecation.",
        "status": 400
      }
    }
  }
}

Policy Configuration

name <string> - The name of your policy instance. This is used as a reference in your routes.
policyType <string> - The identifier of the policy. This is used by the Zuplo UI. Value should be brownout-inbound.
handler.export <string> - The name of the exported type. Value should be BrownoutInboundPolicy.
handler.module <string> - The module containing the policy. Value should be $import(@zuplo/runtime).
handler.options <object> - The options for this policy. See Policy Options below.

Policy Options

The options for this policy are specified below. All properties are optional unless specifically marked as required.

cronSchedule (required) <undefined> - The cron schedule for when this policy is enabled. This can be a single cron string or an array of multiple cron strings.
problem <object> - The problem that is returned in the response body when this policy is enabled.
- type <string> - The type of problem.
- title <string> - The title of problem.
- detail <string> - The detail of problem.
- status <number> - Http status code of the problem.

Using the Policy

Cron Schedules

This policy accepts a single cron schedule or an array of cron schedules. Any time a requests falls withing that schedule the brownout response will be set.

Example schedules could be:

Every Day between 2am and 3am


Code
"cronSchedule": "* 2 * * *"

Every Hour on the hour, and the 15th, 30th, and 45th minutes


Code
"cronSchedule": ["0 * * * *", "15 * * * *", "30 * * * *", "45 * * * *"]

This can also be written as:


Code
"cronSchedule": ["0/15 * * * *"]

Cron Expression Format

This policy uses the linux cron syntax with the addition that you can optionally specify seconds by prepending the minute field with another field.

Code
┌───────────── second (0 - 59, optional)
│ ┌───────────── minute (0 - 59)
│ │ ┌───────────── hour (0 - 23)
│ │ │ ┌───────────── day of month (1 - 31)
│ │ │ │ ┌───────────── month (1 - 12)
│ │ │ │ │ ┌───────────── weekday (0 - 7)
* * * * * *

All linux cron features are supported, including

lists
ranges
ranges in lists
step values
month names (jan,feb,... - case insensitive)
weekday names (mon,tue,... - case insensitive)
time nicknames (@yearly, @annually, @monthly, @weekly, @daily, @hourly - case insensitive)

To test out cron patterns try using a tool like crontab.guru.