Commit 342f9604 authored by Achilleas Pipinellis's avatar Achilleas Pipinellis

Merge branch 'jc-add-docs-for-gitaly-feature-flags' into 'master'

Add development documentation for gitaly feature flags

See merge request gitlab-org/gitlab-ce!25624
parents b0ed83e0 1c2bfc99
......@@ -197,3 +197,82 @@ as a [CI environment variable](../ci/variables/README.md#variables).
---
[Return to Development documentation](README.md)
## Wrapping RPCs in Feature Flags
Here are the steps to gate a new feature in Gitaly behind a feature flag.
### Gitaly
1. Create a package scoped flag name:
```go
var findAllTagsFeatureFlag = "go-find-all-tags"
```
1. Create a switch in the code using the `featureflag` package:
```go
if featureflag.IsEnabled(ctx, findAllTagsFeatureFlag) {
// go implementation
} else {
// ruby implementation
}
```
1. Create prometheus metrics:
```go
var findAllTagsRequests = prometheus.NewCounterVec(
prometheus.CounterOpts{
Name: "gitaly_find_all_tags_requests_total",
Help: "Counter of go vs ruby implementation of FindAllTags",
},
[]string{"implementation"},
)
)
func init() {
prometheus.Register(findAllTagsRequests)
}
if featureflag.IsEnabled(ctx, findAllTagsFeatureFlag) {
findAllTagsRequests.WithLabelValues("go").Inc()
// go implementation
} else {
findAllTagsRequests.WithLabelValues("ruby").Inc()
// ruby impelmentation
}
```
1. Set headers in tests:
```go
import (
"google.golang.org/grpc/metadata"
"gitlab.com/gitlab-org/gitaly/internal/featureflag"
)
//...
md := metadata.New(map[string]string{featureflag.HeaderKey(findAllTagsFeatureFlag): "true"})
ctx = metadata.NewOutgoingContext(context.Background(), md)
c, err = client.FindAllTags(ctx, rpcRequest)
require.NoError(t, err)
```
### Gitlab-Rails
1. Add feature flag to `lib/gitlab/gitaly_client.rb` (in gitlab-rails):
```ruby
SERVER_FEATURE_FLAGS = %w[go-find-all-tags].freeze
```
1. Test in rails console by setting feature flag:
```ruby
Feature.enable('gitaly_go-find-all-tags')
```
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