If you work with containers and work with Kubernetes, Draft makes it easier to deploy your code while you are in the earlier development stages. You use Draft while you are working on your code but before you commit it to version control. The idea is simple:
- You have some code written in something like Node.js, Go or another supported language
- You then use draft create to containerize the application based on Draft packs; several packs come with the tool and provide a Dockerfile and a Helm chart depending on the development language
- You then use draft up to deploy the application to Kubernetes; the application is made accessible via a public URL
Let’s demonstrate how Draft is used, based on a simple Go application that is just a bit more complex than the Go example that comes with Draft. I will use the go-data service that I blogged about earlier. You can find the source code on GitHub. The go-data service is a very simple REST API. By calling the endpoint /data/{deviceid}, it will check if a “device” exists and then actually return no data. Hey, it’s just a sample! The service uses the Gorilla router but also Go Micro to call a device service running in the Kubernetes cluster. If the device service does not run, the data service will just report that the device does not exist.
Note that this post does not cover how to install Draft and its prerequisites like Helm and a Kubernetes Ingress Controller. You will also need a Kubernetes cluster (I used Azure ACS) and a container registry (I used Docker Hub). I installed all client-side components in the Windows 10 Linux shell which works great!
The only thing you need on your development box that has Helm and Draft installed is main.go and an empty glide.yaml file. The first command to run is draft create
This results in several files and folders being created, based on the Golang Draft pack. Draft detected you used Go because of glide.yaml. No Docker container is created at this point.
- Dockerfile: a simple Dockerfile that builds an image based on the golang:onbuild image
- draft.toml: the Draft configuration file that contains the name of the application (set randomly), the namespace to deploy to and if the folder needs to be watched for changes after you do
draft up - chart folder: contains the Helm chart for your application; you might need to make changes here if you want to modify the Kubernetes deployment as we will do soon
When you deploy, Draft will do several things. It will package up the chart and your code and send it to the Draft server-side component running in Kubernetes. It will then instruct Draft to build your container, push it to a configured registry and then install the application in Kubernetes. All those tasks are performed by the Draft server component, not your client!
In my case, after running draft up, I get the following on my prompt (after the build, push and deploy steps):
In my case, the name of the application was set to exacerbated-ragdoll (in draft.toml). Part of what makes Draft so great is that it then makes the service available using that name and the configured domain. That works because of the following:
- During installation of Draft, you need to configure an Ingress Controller in Kubernetes; you can use a Helm chart to make that easy; the Ingress Controller does the magic of mapping the incoming request to the correct application
- When you configure Draft for the first time with
draft inityou can pass the domain (in my case baeke.info); this requires a wildcard A record (e.g. *.baeke.info) that points to the public IP of the Ingress Controller; note that in my case, I used Azure Container Services which makes that IP the public IP of an Azure load balancer that load balances traffic between the Ingress Controller instances (ngnix)
So, with only my source code and a few simple commands, the application was deployed to Kubernetes and made available on the Internet! There is only one small problem here. If you check my source code, you will see that there is no route for /. The Draft pack for Golang includes a livenessProbe on / and a readinessProbe on /. The probes are in deployment.yaml which is the file that defines the Kubernetes deployment. You will need to change the path in livenessProbe and readinessProbe to point to /data/device like so:
- containerPort: {{ .Values.service.internalPort }}
livenessProbe:
httpGet:
path: /data/device
port: {{ .Values.service.internalPort }}
readinessProbe:
httpGet:
path: /data/device
port: {{ .Values.service.internalPort }}
If you already deployed the application but Draft is still watching the folder, you can simply make the above changes and save the deployment.yaml file (in chart/templates). The container will then be rebuilt and the deployment will be updated. When you now check the service with curl, you should get something like:
curl http://exacerbated-ragdoll.baeke.info/data/device1 Device active: false Oh and, no data for you!
To actually make the Go Micro features work, we will have to make another change to deployment.yaml. We will need to add an environment variable that instructs our code to find other services developed with Go Micro using the kubernetes registry:
- name: {{ .Chart.Name }}
image: "{{ .Values.image.registry }}/{{ .Values.image.org }}/{{ .Values.image.name }}:{{ .Values.image.tag }}"
imagePullPolicy: {{ .Values.image.pullPolicy }}
env:
- name: MICRO_REGISTRY
value: kubernetes
To actually test this, use the following command to deploy the device service.
kubectl create -f https://raw.githubusercontent.com/gbaeke/go-device/master/go-device-dep.yaml
You can then check if it works by running the curl command again. It should now return the following:
Device active: true Oh and, no data for you!
Hopefully, you have seen how you can work with Draft from your development box and that you can modify the files generated by Draft to control how your application gets deployed. In our case, we had to modify the health checks to make sure the service can be reached. In addition, we had to add an environment variable because the code uses the Go Micro microservices framework.
baeke.info 