docs: Write a HOW TO guide for using URL Reader

2021-01-13 23:07:59 +01:00
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+---
+id: how-to-guides
+title: TechDocs "HOW TO" guides
+sidebar_label: "HOW TO" guides
+description: TechDocs "HOW TO" guides related to TechDocs
+---
+
+## How to use URL Reader in TechDocs Prepare step?
+
+If TechDocs is configured to generate docs, it will first download the
+repository associated with the `backstage.io/techdocs-ref` annotation defined in
+the Entity's `catalog-info.yaml` file. This is also called the
+[Prepare](./concepts.md#techdocs-preparer) step.
+
+There are two kinds of preparers or two ways of downloading these source files
+
+- Preparer 1: Doing a `git clone` of the repository (also known as Common Git
+  Preparer)
+- Preparer 2: Downloading an archive.zip or equivalent of the repository (also
+  known as URL Reader)
+
+If `backstage.io/techdocs-ref` is equal to any of these -
+
+1. `github:https://githubhost.com/org/repo`
+2. `gitlab:https://gitlabhost.com/org/repo`
+3. `bitbucket:https://bitbuckethost.com/project/repo`
+4. `azure/api:https://azurehost.com/org/project`
+
+Then Common Git Preparer will be used i.e. a `git clone`. But the URL Reader is
+a much faster way to do this step. Convert the `backstage.io/techdocs-ref`
+values to the following -
+
+1. `url:https://githubhost.com/org/repo/tree/<branch_name>`
+2. `url:https://gitlabhost.com/org/repo/tree/<branch_name>`
+3. `url:https://bitbuckethost.com/project/repo/src/<branch_name>`
+4. `url:https://azurehost.com/organization/project/_git/repository`
+
+Note that you can also provide a path to a non-root directory inside the
+repository which contains the `docs/` directory.
+
+e.g.
+`url:https://github.com/backstage/backstage/tree/master/plugins/techdocs-backend/examples/documented-component`
+
+### Why is URL Reader faster than a git clone?
+
+URL Reader uses the source code hosting provider to download a zip or tarball of
+the repository. The archive does not have any git history attached to it. Also
+it is a compressed file. Hence the file size is significantly smaller than how
+much data git clone has to transfer.
+
+Caveat: Currently TechDocs sites built using URL Reader will be cached for 30
+minutes which means they will not be re-built if new changes are made within 30
+minutes. This cache invalidation will be replaced by commit timestamp based
+implementation very soon.