Stop background processes on failure (#2478)

* Stop background processes on failure

* Exit successfully

* Move trap into dev only

* Move install linkerd up

* Fold dev into run

BUILD.md

@@ -247,12 +247,14 @@ These commands assume working [Go](https://golang.org) and
 
 #### First time setup
 
-Install [Yarn](https://yarnpkg.com) and use it to install dependencies:
+1. Install [Yarn](https://yarnpkg.com) and use it to install dependencies:
 
-```bash
-brew install yarn
-bin/web setup
-```
+    ```bash
+    brew install yarn
+    bin/web setup
+    ```
+
+1. Install Linkerd on a Kubernetes cluster.
 
 #### Run web standalone
 
@@ -264,13 +266,28 @@ The web server will be running on `localhost:8084`.
 
 #### Webpack dev server
 
-To develop with a webpack dev server, run:
+To develop with a webpack dev server:
 
-```bash
-bin/web dev
-```
+1. Start the development server.
 
-Note: you'll want to install Linkerd2 on a Kubernetes cluster first.
+    ```bash
+    bin/web dev
+    ```
+
+    Note: this will start up:
+
+    - `web` on :8084. This is the golang process that serves the dashboard.
+    - `webpack-dev-server` on :8080 to manage rebuilding/reloading of the
+      javascript.
+    - `controller` is port-forwarded from the Kubernetes cluster via `kubectl`
+      on :8085
+    - `grafana` is port-forwarded from the Kubernetes cluster via `kubectl`
+      on :3000
+
+1. Go to [http://localhost:8084](http://localhost:8084) to see everything
+   running.
+
+#### Dependencies
 
 To add a JS dependency:
 

bin/web

@@ -40,22 +40,14 @@ function check-for-linkerd {
 }
 
 function dev {
-  build
-
   while getopts "p:" opt; do
     case "$opt" in
       p) DEV_PORT=$OPTARG
     esac
   done
 
-  check-for-linkerd && (
-    port-forward controller 8085 &
-    port-forward grafana 3000 &
-  )
-
   cd $ROOT/web/app && yarn webpack-dev-server --port $DEV_PORT &
-  cd $ROOT/web && \
-    ../bin/go-run . $*
+  run
 }
 
 function build {
@@ -86,6 +78,11 @@ function port-forward {
 }
 
 function run {
+  # Stop everything in the process group (in the background) whenever the
+  # parent process experiences an error and exits.
+  trap "exit" INT TERM
+  trap "kill 0" EXIT
+
   build
 
   check-for-linkerd && (
@@ -93,8 +90,8 @@ function run {
     port-forward grafana 3000 &
   )
 
-  cd $ROOT/web
-  ../bin/go-run . $*
+  cd $ROOT/web && \
+    ../bin/go-run . $*
 }
 
 function setup {