How can I integrate my local GitLab with Slack to getting notification?

Question

How can I integrate my local GitLab with Slack to getting notification?

Where do I find my slack Webhook?

What's the username?

My GitLab version is: 8.16.4. and all that I need the information for these:

Answer 1

The GitLab Slack notification service has this section about Slack itself:

• Sign in to your Slack team and start a new Incoming WebHooks configuration.
• Select the Slack channel where notifications will be sent to by default. Click the Add Incoming WebHooks integration button to add the configuration.
• Copy the Webhook URL, which we'll use later in the GitLab configuration.

The last point is your webhook url that you can then copy-paste into your GitLab Project > Settings > Integrations.

The OP Majid Parvin adds in the comments:

I had this error:

This app is not allowed to be installed on this team. 
Please ask a Team Admin to approve this app

because I wasn't with my admin account.

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Note that, with GitLab 13.3 (August 2020), there are two evolutions

One regarding Slack:

Links to search results now unfurl in tools like Slack

Unfurling a URL in tools like Slack provides useful context for other team members. In GitLab 13.3, search result pages have updated meta headers to provide a better description when unfurled.

https://about.gitlab.com/images/13_3/unfurl-search.png -- Links to search results now unfurl in tools like Slack

See Documentation and Issue.

The other regarding a new notification system based on "incident tickets", still with GitLab 13.3 (August 2020), free edition:

Create and manage IT Incidents in GitLab

Investigating incidents requires on-call engineers to evaluate different data sources across multiple tools. Assessing metrics, logs, and traces, sharing findings, and updating stakeholders requires engineers to manually aggregate information through screengrabs, copying, and pasting. This work is inefficient and time-consuming, which leads to alert fatigue, increased stress, and low morale.

In 13.3, GitLab is excited to introduce a dedicated list for triaging and managing Incidents in the Operations section of GitLab to help you reduce resolution time. The Incident list provides a high-level summary of the incident, and critical details: when it was created, who is assigned, and the Status Page publication state. Additionally, there are different views organized by status (open, closed, and all) making it easy to identify active incidents.

In GitLab 13.4 and beyond we plan to improve incident response workflows by surfacing related metrics charts, embedding logs, and rendering associated runbooks. To view progress and suggest ideas for future improvements, see the Incident Management epic.

See Documentation and Issue.

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With GitLab 14.0 (June 2021), you also have:

Slack notifications for wiki edits include links to diffs

Slack notifications for wiki edits include links to diffs

Our Slack notification service can notify you when a user edits a wiki page. The Slack message gives you helpful context about the edit, including the project, page name, and the commit message.

Sometimes, however, the commit message doesn’t give enough context, and you need more information about how the content changed.

Now you can click Compare changes in the Slack message to immediately view the diff, saving you time and reducing confusion from ambiguous or incomplete commit messages.

See Documentation and Issue.