chore(cdk): add Dockerfile for toolkit container (aws#1569)

Fixes aws#1302.

.dockerignore

@@ -0,0 +1,2 @@
+.dockerignore
+Dockerfile

CONTRIBUTING.md

@@ -198,6 +198,29 @@ If you also wish to package to all languages, make sure you have all the [toolch
 $ ./pack.sh
 ```
 
+### Full Docker build
+
+Clone the repo:
+
+```console
+$ git clone git@github.com/awslabs/aws-cdk
+$ cd aws-cdk
+```
+
+If you already have a local repo and you want a fresh build, run `git clean -fdx` from the root.
+
+Build the docker image:
+
+```console
+$ docker build -t aws-cdk .
+```
+
+This allows you to run the CDK in a CDK-compatible directory with a command like:
+
+```console
+$ docker run -v $(pwd):/app -w /app aws-cdk <CDK ARGS>
+```
+
 ### Partial build
 
 In many cases, you don't really need to build the entire project. Say you want to work on the `@aws-cdk/aws-ec2` module:
@@ -268,7 +291,7 @@ $ BUILD_DOCS_DEV=1 ./build-docs.sh
 ### Tooling Assists
 #### Jetbrains (WebStorm/IntelliJ)
 This project uses lerna and utilizes symlinks inside nested node_modules directories. You may encounter an issue during
-indexing where the IDE attempts to index these directories and keeps following links until the process runs out of 
+indexing where the IDE attempts to index these directories and keeps following links until the process runs out of
 available memory and crashes. To fix this, you can run ```node ./scripts/jetbrains-remove-node-modules.js``` to exclude
 these directories.
 

Dockerfile

@@ -0,0 +1,20 @@
+FROM node:8.15-alpine
+
+WORKDIR /app
+
+RUN apk add --update \
+    bash \
+    git \
+    rsync \
+    zip \
+    python3 \
+    python3-dev \
+    py3-setuptools \
+ && rm -rf /var/cache/apk/*
+
+COPY . .
+
+RUN ./build.sh \
+ && ./link-all.sh
+
+ENTRYPOINT ["/app/node_modules/.bin/cdk"]