Dockerfile
This is a file called Dockerfile which allows us to specify how to build a container. Let's have a look at one:
FROM <image>
This means we pull down an image that we base this on, this is usually an image that is based on an OS like Ubuntu for example. Let's take an image where nodejs is pre installed, like so:
FROM node:8
Now let's set a working directory for our app. This is where all the files will be placed. It's done with the WORKDIR command:
WORKDIR /usr/src/app
Next step is copying over the package.json file as it contains instructions for what NPM modules our app needs, like so:
COPY package*.json ./
After that we need to actually install the libraries like so:
RUN npm install
Now let's copy the entire app. We want all the files to end up in our work directory so we write:
COPY . .
from current directory into WORKDIR
Now let's expose a port in which you can find our application:
EXPOSE 8080
Lastly start up our app by calling
CMD ["npm", "start"]
Let's show the Dockerfile in its entirety:
FROM node:8
WORKDIR /usr/src/app
COPY package*.json ./
RUN npm install
# Bundle app source
COPY . .
EXPOSE 8080
CMD [ "npm ", "start" ]
build
Next step is to build our Dockerfile and create an image. Once we have an image we can start a container from it. For that we will use the docker build command, like so:
docker build -t <your username>/node-web-app .
We use the -t to tag, give it a name. Let's inspect by running
docker images
This should list our image with the name we tagged it with.
run
Now let's create a container from our image so we can actually is ut for something. We do that with the following command:
docker run -p 49160:8080 -d <your username>/node-web-app
Let's break apart this a bit -p means that we are creating a bridge between our host OS and our container. What we are saying is which port on our container should connect to what port in the container. The syntax looks like this:
-p <port on our system>:<exposed container port>
By typing
-p 49160:8080
We are saying we can find the app running at http://localhost:49160
OR we can use curl, like so:
curl -i localhost:49160
We have already said in app.js that we aim to run our express server on port 8080 and expose the same port in the Dockerfile