pennant

Pennant Feature Flags

Pennant is a powerful dark-launch utility designed for maximum flexibility and performance.

Getting Started

Building and running pennant:

% brew install consul
% consul agent -dev -advertise 127.0.0.1
% git clone pennant.git
% go build && ./pennant server

Example flag

{
  "name": "red_button",
  "description": "Makes the button on the home page red",
  "default": false,
  "policies": [
     {
      "comment": "Everybody whose username starts with 'foo'",
      "rules": "user_username =~ '^foo'"
     },
     {
      "comment": "and some volunteers",
      "rules": "user_id in (10, 11, 13)"
     },
     {
      "comment": "Also 10% of rando users",
      "rules": "pct(user_username) <= 10"
     }
  ]
}

Test a flag without a server

pennant test -f tests/data/flag1.json -d tests/data/data1.json

CLI

Create or update a flag

$ pennant update -f tests/data/flag1.json
- or -
$ pennant update '{"name":"red_button","description":....}'
- or -
$ cat tests/data/flag1.json | pennant update -

Name        Description                            DefaultValue
----------  -------------------------------------  ------------
red_button  Makes the button on the home page red  false

Rule                      Comment
------------------------  ------------------------------------------
user_username =~ '^foo'   Everybody whose username starts with 'foo'
user_id in (10, 11, 13)   and some volunteers
pct(user_username) <= 10  Also 10% of rando users

List flags

% pennant list
Name
----------
red_button

Get flag details

$ pennant show red_button
Name        Description                            DefaultValue
----------  -------------------------------------  ------------
red_button  Makes the button on the home page red  false

Rule                      Comment
------------------------  ------------------------------------------
user_username =~ '^foo'   Everybody whose username starts with 'foo'
user_id in (10, 11, 13)   and some volunteers
pct(user_username) <= 10  Also 10% of rando users

Check whether a flag is enabled

$ pennant value red_button '{"user_id": 10}'
- or -
$ pennant value red_button -f document.json
- or -
$ cat document.json | pennant value red_button -
Flag        Status
----------  -------
red_button  enabled

Delete a flag

$ pennant delete red_button
red_button deleted

API

Roadmap

V1 milestones:

• ✓ Pluggable storage backends, ships with consul and in-memory support
• ✓ GRPC and REST query interfaces
• ✓ REST flag management interfaces
• ✓ Watches for consul value changes
• ✓ Bundled percentage calculator
• ✓ Supports arbitrary expressions for en/disabling flags
• ✓ Client and server in single binary
• Ships metrics to StatsD
• FlagGroup - evaluate multiple flags in a single query

V2:

• More drivers - redis, etcd, filesystem
• Authentication
• Prometheus compatible stats
• Query results caching, perf improvements
• GRPC flag management interface

Further reading on feature flags

• http://featureflags.io/
• https://engineering.instagram.com/flexible-feature-control-at-instagram-a7d3417658df