feature

Overview ¶

Package feature provides feature flagging capabilities for InfluxDB servers. This document describes this package and how it is used to control experimental features in `influxd`.

Flags are configured in `flags.yml` at the top of this repository. Running `make flags` generates Go code based on this configuration to programmatically test flag values in a given request context. Boolean flags are the most common case, but integers, floats and strings are supported for more complicated experiments.

The `Flagger` interface is the crux of this package. It computes a map of feature flag values for a given request context. The default implementation always returns the flag default configured in `flags.yml`. The override implementation allows an operator to override feature flag defaults at startup. Changing these overrides requires a restart.

In `influxd`, a `Flagger` instance is provided to a `Handler` middleware configured to intercept all API requests and annotate their request context with a map of feature flags.

A flag can opt in to be exposed externally in `flags.yml`. If exposed, this flag will be included in the response from the `/api/v2/flags` endpoint. This allows the UI and other API clients to control their behavior according to the flag in addition to the server itself.

A concrete example to illustrate the above:

I have a feature called "My Feature" that will involve turning on new code in both the UI and the server.

First, I add an entry to `flags.yml`.

```yaml

• name: My Feature description: My feature is awesome key: myFeature default: false expose: true contact: My Name

```

My flag type is inferred to be boolean by my default of `false` when I run `make flags` and the `feature` package now includes `func MyFeature() BoolFlag`.

I use this to control my backend code with ¶

```go

if feature.MyFeature.Enabled(ctx) {
  // new code...
} else {

  // new code...
}

```

and the `/api/v2/flags` response provides the same information to the frontend.

```json

{
  "myFeature": false
}

```

While `false` by default, I can turn on my experimental feature by starting my server with a flag override.

``` env INFLUXD_FEATURE_FLAGS="{\"flag1\":\value1\",\"key2\":\"value2\"}" influxd ```

``` influxd --feature-flags flag1=value1,flag2=value2 ```