feat: hot-reload functionality for local k8s

When the local-kubernetes provider is used, container modules can now be
configured to hot-reload their running services when the module's
sources change (i.e. without redeploying).

Services that can be run with an FS watcher that automatically applies
changed sources to the running application (e.g. nodemon and many other
web app frameworks) are a natural fit for this feature.

docs/reference/config.md

@@ -553,6 +553,14 @@ module:
         # Optional.
         tcpPort:
 
+      # If this module uses the `hotReload` field, the container will be run with these arguments
+      # instead of those in `command` while a Garden command with the -w (watch) flag, or `garden
+      # dev`, is running.
+      #
+      # Optional.
+      hotReloadCommand: 
+        -
+
       # List of ports that the service container exposes.
       #
       # Optional.
@@ -634,5 +642,31 @@ module:
       # Optional.
       env: 
         {}
+
+  # When this field is used, the files or directories specified within are automatically synced
+  # into the running container when they're modified. Additionally, any of this module's services
+  # that define a `hotReloadCommand` will be run with that command instead of the one specified in
+  # their `command` field. This behavior is only active while a Garden command with the -w (watch)
+  # flag, or `garden dev`, is running.
+  #
+  # Optional.
+  hotReload: 
+    # Specify one or more source files or directories to automatically sync into the running
+    # container.
+    #
+    # Required.
+    sync: 
+      - # POSIX-style path of the directory to sync to the target, relative to the module's
+        # top-level directory. Must be a relative path if provided. Defaults to the module's
+        # top-level directory if no value is provided.
+        #
+        # Optional.
+        source: .
+
+        # POSIX-style absolute path to sync the directory to inside the container. The root path
+        # (i.e. "/") is not allowed.
+        #
+        # Required.
+        target:
 ```
 

examples/hot-reload/build-dependant/.dockerignore

@@ -0,0 +1,4 @@
+node_modules
+Dockerfile
+garden.yml
+app.yaml

examples/hot-reload/build-dependant/Dockerfile

@@ -0,0 +1,12 @@
+FROM node:9-alpine
+
+ENV PORT=8080
+EXPOSE ${PORT}
+
+ADD . /app
+WORKDIR /app
+
+RUN npm install -g nodemon
+RUN npm install
+
+CMD ["npm", "start"]

examples/hot-reload/build-dependant/app.js

@@ -0,0 +1,14 @@
+const express = require("express")
+
+const app = express()
+
+app.get("/dependant", (req, res) => {
+  res.json({message: "Build dependant"})
+})
+
+// This is the path GAE uses for health checks
+app.get("/_ah/health", (req, res) => {
+  res.sendStatus(200)
+})
+
+module.exports = { app }

examples/hot-reload/build-dependant/garden.yml

@@ -0,0 +1,20 @@
+module:
+  description: Build dependant
+  name: build-dependant
+  type: container
+  services:
+    - name: build-dependant
+      command: [npm, start]
+      ports:
+        - name: http
+          containerPort: 8080
+      ingresses:
+        - path: /dependant
+          port: http
+      healthCheck:
+        httpGet:
+          path: /_ah/health
+          port: http
+  build:
+    dependencies:
+      - good-morning

examples/hot-reload/build-dependant/main.js

@@ -0,0 +1,3 @@
+const { app } = require("./app")
+
+app.listen(process.env.PORT, "0.0.0.0", () => console.log("App started"))