Merge branch '10341-enable-k8s-attach-by-default' into 'master'

Enable kubernetes attach strategy by default

Closes #10341

See merge request gitlab-org/gitlab-runner!2955

Author: Steve Azzopardi

docs/configuration/feature-flags.md

@@ -41,7 +41,7 @@ The flags are defined in `./helpers/featureflags/flags.go` file.
 |--------------|---------------|------------|--------------------|-------------|
 | `FF_CMD_DISABLE_DELAYED_ERROR_LEVEL_EXPANSION` | `false` | ✗ |  | Disables [EnableDelayedExpansion](https://ss64.com/nt/delayedexpansion.html) for error checking for when using [Window Batch](../shells/index.md#windows-batch) shell |
 | `FF_NETWORK_PER_BUILD` | `false` | ✗ |  | Enables creation of a Docker [network per build](../executors/docker.md#networking) with the `docker` executor |
-| `FF_USE_LEGACY_KUBERNETES_EXECUTION_STRATEGY` | `true` | ✗ |  | When set to `false` disables execution of remote Kubernetes commands through `exec` in favor of `attach` to solve problems like [#4119](https://gitlab.com/gitlab-org/gitlab-runner/-/issues/4119) |
+| `FF_USE_LEGACY_KUBERNETES_EXECUTION_STRATEGY` | `false` | ✗ |  | When set to `false` disables execution of remote Kubernetes commands through `exec` in favor of `attach` to solve problems like [#4119](https://gitlab.com/gitlab-org/gitlab-runner/-/issues/4119) |
 | `FF_USE_DIRECT_DOWNLOAD` | `true` | ✗ |  | When set to `true` Runner tries to direct-download all artifacts instead of proxying through GitLab on a first try. Enabling might result in a download failures due to problem validating TLS certificate of Object Storage if it is enabled by GitLab. See [Self-signed certificates or custom Certification Authorities](tls-self-signed.md) |
 | `FF_SKIP_NOOP_BUILD_STAGES` | `true` | ✗ |  | When set to `false` all build stages are executed even if running them has no effect |
 | `FF_USE_FASTZIP` | `false` | ✗ |  | Fastzip is a performant archiver for cache/artifact archiving and extraction |

docs/executors/kubernetes.md

@@ -876,13 +876,17 @@ For more information, see [Building images with kaniko and GitLab CI/CD](https:/
 
 ## Job execution
 
-At the moment we are using `kube exec` to run the scripts, which relies on
-having a stable network connection between the Runner and the pod for the duration of the command.
-This leads to problems like [Job marked as success midway](https://gitlab.com/gitlab-org/gitlab-runner/-/issues/4119).
-If you are experiencing this problem turn off the feature flag [`FF_USE_LEGACY_KUBERNETES_EXECUTION_STRATEGY`](../configuration/feature-flags.md#available-feature-flags)
-to use `kube attach` for script execution, which is more stable.
+> - [Introduced](https://gitlab.com/gitlab-org/gitlab-runner/-/merge_requests/1775) in GitLab Runner 12.9.
+> - [Behind a feature flag `FF_USE_LEGACY_KUBERNETES_EXECUTION_STRATEGY`](../configuration/feature-flags.md#available-feature-flags), enabled by default.
+> - [Using attach by default](https://gitlab.com/gitlab-org/gitlab-runner/-/issues/10341) in GitLab Runner 14.0.
 
-We are rolling this out slowly and have plans to enable the `kube attach` behavior by default in future release, please follow [#10341](https://gitlab.com/gitlab-org/gitlab-runner/-/issues/10341) for updates.
+GitLab Runner uses `kube attach` instead of `kube exec` by default. This should avoid problems such as [Job marked as success midway](https://gitlab.com/gitlab-org/gitlab-runner/-/issues/4119)
+in environments with unstable network.
+
+If you are experiencing problems since updating to GitLab Runner 14.0, toggle the feature flag [`FF_USE_LEGACY_KUBERNETES_EXECUTION_STRATEGY`](../configuration/feature-flags.md#available-feature-flags)
+to `true` and [submit an issue](https://gitlab.com/gitlab-org/gitlab-runner/-/issues/new).
+
+Follow [#27976](https://gitlab.com/gitlab-org/gitlab-runner/-/issues/27976) for progress regarding legacy execution strategy removal.
 
 ## Troubleshooting
 

helpers/featureflags/flags.go

@@ -54,7 +54,7 @@ var flags = []FeatureFlag{
 	},
 	{
 		Name:            UseLegacyKubernetesExecutionStrategy,
-		DefaultValue:    true,
+		DefaultValue:    false,
 		Deprecated:      false,
 		ToBeRemovedWith: "",
 		Description: "When set to `false` disables execution of remote Kubernetes commands through `exec` in " +