Fixed broken external links

Related to: https://gitlab.com/gitlab-org/technical-writing/-/issues/492

doc/development/contributing/merge_request_workflow.md

@@ -255,7 +255,7 @@ requirements.
 1. The change is tested in a review app where possible and if appropriate.
 1. The new feature does not degrade the user experience of the product.
 1. The change is evaluated to [limit the impact of far-reaching work](https://about.gitlab.com/handbook/engineering/development/#reducing-the-impact-of-far-reaching-work).
-1. An agreed-upon [rollout plan](https://about.gitlab.com/handbook/engineering/development/processes/rollout-plans).  
+1. An agreed-upon [rollout plan](https://about.gitlab.com/handbook/engineering/development/processes/rollout-plans/).  
 1. Merged by a project maintainer.
 
 ### Production use

doc/development/database/multiple_databases.md

@@ -508,7 +508,7 @@ end
 ```
 
 Don't hesitate to reach out to the
-[sharding group](https://about.gitlab.com/handbook/engineering/development/enablement/sharding)
+[sharding group](https://about.gitlab.com/handbook/engineering/development/enablement/sharding/)
 for advice.
 
 ## `config/database.yml`

doc/development/feature_flags/index.md

@@ -21,7 +21,7 @@ All newly-introduced feature flags should be [disabled by default](https://about
 NOTE:
 This document is the subject of continued work as part of an epic to [improve internal usage of Feature Flags](https://gitlab.com/groups/gitlab-org/-/epics/3551). Raise any suggestions as new issues and attach them to the epic.
 
-For an [overview of the feature flag lifecycle](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#feature-flag-lifecycle), or if you need help deciding [if you should use a feature flag](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#when-to-use-feature-flags) or not, please see the [feature flag lifecycle](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle) handbook page.
+For an [overview of the feature flag lifecycle](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#feature-flag-lifecycle), or if you need help deciding [if you should use a feature flag](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/#when-to-use-feature-flags) or not, please see the [feature flag lifecycle](https://about.gitlab.com/handbook/product-development-flow/feature-flag-lifecycle/) handbook page.
 
 ## When to use feature flags
 

doc/ssh/index.md

@@ -326,7 +326,7 @@ If you are using [EGit](https://www.eclipse.org/egit/), you can [add your SSH ke
 
 ## Use SSH on Microsoft Windows
 
-If you're running Windows 10, you can either use the [Windows Subsystem for Linux (WSL)](https://docs.microsoft.com/en-us/windows/wsl/install-win10)
+If you're running Windows 10, you can either use the [Windows Subsystem for Linux (WSL)](https://docs.microsoft.com/en-us/windows/wsl/install)
 with [WSL 2](https://docs.microsoft.com/en-us/windows/wsl/install-win10#update-to-wsl-2) which
 has both `git` and `ssh` preinstalled, or install [Git for Windows](https://gitforwindows.org) to
 use SSH through Powershell.

doc/topics/autodevops/requirements.md

@@ -160,7 +160,7 @@ To make full use of Auto DevOps with Kubernetes, you need:
 
 - **cert-manager** (optional, for TLS/HTTPS)
 
-  To enable HTTPS endpoints for your application, you can [install cert-manager](https://cert-manager.io/docs/installation/kubernetes/),
+  To enable HTTPS endpoints for your application, you can [install cert-manager](https://cert-manager.io/docs/installation/supported-releases/),
   a native Kubernetes certificate management controller that helps with issuing
   certificates. Installing cert-manager on your cluster issues a
   [Let's Encrypt](https://letsencrypt.org/) certificate and ensures the

doc/update/plan_your_upgrade.md

@@ -173,7 +173,7 @@ If anything doesn't go as planned:
   - [`kubesos`](https://gitlab.com/gitlab-com/support/toolbox/kubesos/) if
     you installed GitLab using the Helm Charts.
 - For support:
-  - [Contact GitLab Support](https://support.gitlab.com) and,
+  - [Contact GitLab Support](https://support.gitlab.com/hc) and,
     if you have one, your Technical Account Manager.
   - If [the situation qualifies](https://about.gitlab.com/support/#definitions-of-support-impact)
     and [your plan includes emergency support](https://about.gitlab.com/support/#priority-support),

doc/user/project/integrations/github.md

@@ -18,7 +18,7 @@ and is automatically configured on [GitHub import](../../../integration/github.m
 
 ## Configuration
 
-This integration requires a [GitHub API token](https://docs.github.com/en/github/authenticating-to-github/keeping-your-account-and-data-secure/creating-a-personal-access-token)
+This integration requires a [GitHub API token](https://docs.github.com/en/authentication/keeping-your-account-and-data-secure/creating-a-personal-access-token)
 with `repo:status` access granted.
 
 Complete these steps on GitHub:

doc/user/project/integrations/mattermost_slash_commands.md

@@ -16,7 +16,7 @@ separately configured [Mattermost Notifications Service](mattermost.md).
 
 ## Prerequisites
 
-Mattermost [3.4 or later](https://mattermost.com/blog/category/releases/) is required.
+Mattermost [3.4 or later](https://mattermost.com/blog/category/platform/releases/) is required.
 GitLab provides different methods of configuring Mattermost slash commands, depending
 on your configuration:
 

doc/user/project/integrations/prometheus.md

@@ -75,7 +75,7 @@ service account can be found at Google's documentation for
 1. (Optional) In **Google IAP Service Account JSON**, provide the contents of the
    Service Account credentials file that is authorized to access the Prometheus resource.
    The JSON key `token_credential_uri` is discarded to prevent
-   [Server-side Request Forgery (SSRF)](https://www.hackerone.com/blog-How-To-Server-Side-Request-Forgery-SSRF).
+   [Server-side Request Forgery (SSRF)](https://www.hackerone.com/application-security/how-server-side-request-forgery-ssrf).
 1. Click **Save changes**.
 
 ![Configure Prometheus Service](img/prometheus_manual_configuration_v13_2.png)