Deploy
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Preview deploys
Preview deploys
With previews enabled, opening a pull request builds a complete environment on its own URL, forked database included, so a change can be reviewed running before it merges.
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What a preview gives you
When a pull request is opened against the service's connected branch, Naijacloud builds the branch and publishes it on a URL of its own. Reviewers open the link and use the change instead of reading a diff and imagining it.
Each preview is a full environment: its own container, its own variables, and, where the service has a database attached, its own forked copy of that database.
Why the database is forked
A preview that shares production data is not safe to review: a migration in the branch would run against real rows, and a test order would land in real reporting.
Forking gives the preview a copy to work against, so you can run migrations, insert fixtures, and delete things freely. The copy is discarded with the preview.
A fork is a copy taken when the preview is created. It does not receive later writes from the source database, and its own writes never flow back.
Enabling previews
Previews are toggled per service, from its Settings tab.
With the toggle on, previews are created for pull requests from that point onwards. Existing open pull requests get a preview on their next push.
Lifecycle
| Event | What happens |
|---|---|
| Pull request opened | Preview is built and published on its own URL |
| New commit pushed | Preview rebuilds at that commit |
| Pull request merged | Preview and its database copy are removed |
| Pull request closed | Preview and its database copy are removed |
Because previews are torn down automatically, they do not accumulate cost after a branch is done.
Variables in a preview
A preview inherits the variables of the environment its base branch deploys to, with the database connection details replaced by those of its forked copy.
If a value must differ in previews, say a sandbox payment key rather than a live one, set it on the environment the previews inherit from. The live credentials are then never present in a preview at all.
Preview URLs are unlisted but publicly reachable, so anyone with the link can open one. Keep that in mind for a change that exposes something not yet announced.