How To Run Go RESTful Service In Docker On Mac OS X

Docker is the most popular container technology nowadays and many developers run it locally on their computers and laptops. Docker can run natively on Ubuntu and some other Linux distributions, but not on Mac OS X yet. In this post we will learn how to run a simple Go RESTful service in Docker on Mac. In our example we will piggy back on a simple RESTful service developed in an earlier posts How To Create A Simple RESTful Service In Go.

Docker installation on Mac OS X

If you do not have Docker (and Docker Machine) installed, please follow official Mac OS X installation instruction.

Creating Docker image

First we need to create a Docker image with our RESTful service.

mkdir restful-go  
cd restful-go  
touch Dockerfile  

Docker image is built from Dockerfile. Edit the Dockerfile with your favourite editor so that it has the following content:

FROM golang:latest

RUN go get github.com/upitau/goinbigdata/examples/hellorest

CMD /go/bin/hellorest

EXPOSE 8080  

This simple Dockerfile tells Docker to:

  1. Pull latest Golang image from Docker Hub
  2. Install github.com/upitau/goinbigdata/examples/hellorest go package with "Hello World" RESTful service
  3. Run the RESTful service
  4. Expose port 8080 used by the RESTful service

Detailed description of Dockerfile commands can be found in official reference.

Now we are ready to build a Docker image:

restful-go> docker build -t restful-hello .  

This tells Docker to build image with name restful-hello from Dockerfile in current directory (denoted by dot).

Output:

Sending build context to Docker daemon 2.048 kB  
Step 1 : FROM golang:latest  
 ---> bf9e64d14fb2
Step 2 : RUN go get github.com/upitau/goinbigdata/examples/hellorest  
 ---> Running in e8f0d707afee
 ---> 564ff81a2c21
Removing intermediate container e8f0d707afee  
Step 3 : CMD /go/bin/hellorest  
 ---> Running in 41a6b941e7c5
 ---> dd3a894026df
Removing intermediate container 41a6b941e7c5  
Step 4 : EXPOSE 8080  
 ---> Running in 9f5af3905479
 ---> de4e96d82b57
Removing intermediate container 9f5af3905479  
Successfully built de4e96d82b57  

We can now see our restful-hello Docker image among others:

docker images  

Output:

REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE  
restful-hello       latest              de4e96d82b57        40 seconds ago      751.6 MB  
golang              latest              bf9e64d14fb2        6 days ago          744 MB  
nginx               latest              69203b7cd029        12 days ago         134.6 MB  

Running Go RESTful service in Docker

When image is created, running Docker container is as simple as:

docker run -d -p 8080:8080 restful-hello  

Output:

10efaf236e68c715cacfd0394bbec940a2a18da655afd754c4a2fec0d3293574  

This command tells Docker to run a new container based on image restful-hello. Param -d tells Docker to run container as daemon. Param -p maps port 8080 of Docker host to the same port on Docker container. This port mapping is necessary. When we will try to connect to RESTful service later, we will connect to Docker host which, in its turn, will relay our request to Docker container. The output is an id of created container.

Let's check that our Docker container is up and running:

docker ps  

Output:

CONTAINER ID        IMAGE               COMMAND                  CREATED             STATUS              PORTS                    NAMES  
10efaf236e68        restful-hello       "/bin/sh -c /go/bin/h"   20 seconds ago      Up 19 seconds       0.0.0.0:8080->8080/tcp   sharp_hodgkin  

Our RESTful service is up and running, and ready to serve.

Calling restful-hello service

As we noted earlier, to call our service we need to call Docker host. On Linux, Docker host is the same as localhost, but on Mac it is a virtual machine running in VirtualBox. Therefore, the first thing we need to do is to get ip address of Docker host.

docker-machine ip  

Output:

192.168.99.100  

Now, when we know the ip, we can finally call our service:

GET http://192.168.99.100:8080/hello  

Output:

Hello, Stranger  

Bottom line

Running RESTful service in Docker on Mac OS X requires a bit more effort than running on Ubuntu, but is still quite easy. First, we need to create a Docker image with our service. And then create and run a Docker container based on the image.

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