Node versioning

This page discusses a number of aspects of Node versioning on App Service

Installation structure

Root node

There is a 'root' Node installed directly in D:\Program Files (x86)\nodejs, which is an ancient version: v0.6.20. There is no legitimate use for this version.

Improvement: we should clean this up.

Selection of Node versions under that

Then under that folder, there is one subfolder for each supported version. e.g. v8.8.1 is in D:\Program Files (x86)\nodejs\8.8.1.

Removed versions

When we need to remove a version from the VM, instead of just deleting the folder, we create a symlink to a different version, so that apps pointing to the deleted version have a chance to continue working.

You can see this by running 'dir' under D:\Program Files (x86)\nodejs in Kudu Console. e.g.

10/26/2017  04:04 AM    <SYMLINKD>     5.8.0 [D:\Program Files (x86)\nodejs\6.11.2]
10/26/2017  04:04 AM    <SYMLINKD>     5.9.1 [D:\Program Files (x86)\nodejs\6.11.2]

Improvement: instead of relying on symlinks, it may be better to have smart behavior on App Starts that picks a best match version.

The WEBSITE_NODE_DEFAULT_VERSION App Setting

Case where it's missing

In the absence of this app setting, we use the root Node, which is v0.6.20. This is bad.

Improvement: instead of using the default, it should use the latest. Current behavior was to avoid a breaking change earlier. But now that v0.6.20 is for all practical purpose unusable, we can change the behavior.

Case where it points to a version that doesn't exist

If the version doesn't exist, the site is 100% busted with 500.

Improvement: instead of just failing, it should use the closest match

Semver range support

Today, WEBSITE_NODE_DEFAULT_VERSION must be set to an exact value, e.g. 8.8.1

Improvement: it could support some subset of semver ranges, e.g. ~8 for the latest 8.x.