flagd

README

Flagd

Flagd is a simple command line tool for fetching and presenting feature flags to services. It is designed to conform to OpenFeature schema for flag definitions.

Example usage

1. Generate the prerequisites make generate
2. Build the flagd binary: make build
3. Start the process: ./flagd start -f config/samples/example_flags.json --service-provider http --sync-provider filepath

This now provides an accessible http endpoint for the flags:

$ curl -X POST "localhost:8080/flags/myBoolFlag/resolve/boolean"
// {"value":true,"reason":"STATIC","variant":"on"}

$ curl -X POST "localhost:8080/flags/myStringFlag/resolve/string"
// {"value":"val1","reason":"STATIC","variant":"key1"}

$ curl -X POST "localhost:8080/flags/myNumberFlag/resolve/number"
// {"value":1,"reason":"STATIC","variant":"one"}

$ curl -X POST "localhost:8080/flags/myObjectFlag/resolve/object"
// {"value":{"key":"val"},"reason":"STATIC","variant":"object1"}

$ curl -X POST "localhost:8080/flags/isColorYellow/resolve/boolean" -d '{"color": "yellow"}'
// {"value":true,"reason":"TARGETING_MATCH","variant":"on"}

$ curl -X POST "localhost:8080/flags/myBoolFlag/resolve/string"
// {"error_code":"TYPE_MISMATCH","reason":"ERROR"}

$ curl -X POST "localhost:8080/flags/aMissingFlag/resolve/string"
// {"error_code":"FLAG_NOT_FOUND","reason":"ERROR"}

Multiple source example

Multiple providers can be supplied as the following:

./flagd start -f config/samples/example_flags.json -f config/samples/example_flags_secondary.json --service-provider http --sync-provider filepath

In case of collision between flags definition the priority goes to the later (e.g. example_flags < example_flags_secondary).

Installation

Systemd

To install as a systemd service run sudo make install this will place the binary by default in /usr/local/bin

There will also be a default provider and sync enabled ( http / filepath ) both of which can be modified in the flagd.service.

Validation can be run with systemctl status flagd And result similar to below will be seen

● flagd.service - "A generic feature flag daemon"
     Loaded: loaded (/etc/systemd/system/flagd.service; disabled; vendor preset: enabled)
     Active: active (running) since Mon 2022-05-30 12:19:55 BST; 5min ago
   Main PID: 64610 (flagd)
      Tasks: 7 (limit: 4572)
     Memory: 1.4M
     CGroup: /system.slice/flagd.service
             └─64610 /usr/local/bin/flagd start -f=/etc/flagd/flags.json

May 30 12:19:55 foo systemd[1]: Started "A generic feature flag daemon".

Running in a container

1. IMG=flagd-local make docker-build
2. docker run -p 8080:8080 -it flagd-local start --uri ./examples/example_flags.json

Targeting Rules

The flag object has a field named "targeting", this can be populated with a JsonLogic rule. Any data in the body of a flag evaluation call is processed by the JsonLogic rule to determine the result of flag evaluation. If this result is null or an invalid (undefined) variant then the default variant is returned.

JsonLogic provides a playground for evaluating your rules against data.

Example

A flag is defined as such:

{
  "flags": {
    "isColorYellowFlag": {
      "state": "ENABLED",
      "variants": {
        "on": true,
        "off": false
      },
      "defaultVariant": "off",
      "targeting": {
        "if": [
          {
            "==": [
              {
                "var": [
                  "color"
                ]
              },
              "yellow"
            ]
          },
          "on",
          "off"
        ]
      }
    }
  }
}

The rule provided returns "on" if var color == "yellow" and "off" otherwise:

$ curl -X POST "localhost:8080/flags/isColorYellow/resolve/boolean" -d '{"color": "yellow"}'

returns

{"value":true,"reason":"TARGETING_MATCH","variant":"on"}

whereas

$ curl -X POST "localhost:8080/flags/isColorYellow/resolve/boolean" -d '{"color": "white"}'

returns

{"value":true,"reason":"TARGETING_MATCH","variant":"off"}