When the local-kubernetes or kubernetes provider is used, container modules can be configured to hot-reload their running services when the module's sources change (i.e. without redeploying). In essence, hot-reloading copies syncs files into the appropriate running containers (local or remote) when code is changed by the user, and optionally runs a post-sync command inside the container.

For example, services that can be run with a file system watcher that automatically updates the running application process when sources change (e.g. nodemon, Django, Ruby on Rails, and many other web app frameworks) are a natural fit for this feature.

Usage

Currently, services are only deployed with hot reloading enabled when their names are passed to the --hot option via garden deploy or garden dev commands (e.g. garden dev --hot=foo-service,bar-service). If these services don't belong to a module defining a hotReload configuration (see below for an example), an error will be thrown if their names are passed to the --hot option.

You can also pass * (e.g. --hot=*/--hot-reload=*) to deploy all compatible services with hot reloading enabled (i.e. all services belonging to a module that defines a hotReload configuration).

Subsequently deploying a service belonging to a module configured for hot reloading via garden deploy (without the watch flag) results in the service being redeployed in standard configuration.

Since hot reloading is triggered via Garden's file system watcher, hot reloading only occurs while a watch-mode Garden command is running.

Basic example

Following is an example of a module configured for hot reloading:

kind: Module
description: My Test Service
name: test-service
type: container
hotReload:
  sync:
  - target: /app
services:
  - name: test-service
    args: [npm, start]             # runs `node main.js`
    hotReloadArgs: [npm, run, dev] # runs `nodemon main.js`

In the above, the hotReload field specifies the destination path inside the running container that the module's (top-level) directory (where its garden.yml resides) is synced to.

Note that only files tracked in version control are synced, e.g. respecting .gitignore.

If a source is specified along with target, that subpath in the module's directory is synced to the target instead of the default of syncing the module's top-level directory.

You can configure several such source/target pairs, but note that the source paths must be disjoint, i.e. a source path may not be a subdirectory of another source path within the same module. Here's an example:

  hotReload:
    sync:
      - source: foo
        target: /app/foo
      - source: bar
        target: /app/bar

Lastly, hotReloadArgs specifies the arguments to use to run the container (when deployed with hot reloading enabled). If no hotReloadArgs are specified, args is also used to run the container when the service is deployed with hot reloading enabled

Adding a postSyncCommand

A postSyncCommand can also be added to a module's hot reload configuration. This command is executed inside the running container during each hot reload, after syncing is completed (as the name suggests).

Following is a snippet from the hot-reload-post-sync-command example project. Here, a postSyncCommand is used to touch a file, updating its modification time. This way, nodemon only has to watch one file to keep the running application up to date. See the hot-reload-post-sync-command example for more details and a fuller discussion.

kind: Module
description: Node greeting service
name: node-service
type: container
hotReload:
  sync:
    - target: /app
  postSyncCommand: [touch, /app/hotreloadfile]
services:
  - name: node-service
    args: [npm, start]
    hotReloadArgs: [npm, run, dev] # Runs modemon main.js --watch hotreloadfile
  ...