Local development workflow with Tilt and Carvel

Software development often involves a cycle of making a code change, running unit tests, building an image then deploying a container to Docker or Kubernetes. Tilt is a tool that can help to automate the local workflow of

code -> build -> deploy -> test

In this article, we will take a tour of the capabilities of Tilt and demonstrate how it can be integrated with Carvel tools.

What is Tilt?

Tilt is a command line tool with a built-in server that continuously builds and deploys code by watching for changes. This allows developers to make code changes and run tests without having to manually run commands to deploy the change. This is a great feature for reducing friction when running end-to-end tests during development. Tilt supports deployment to local machine, docker, kubernetes and custom targets.

Tilt is configured using a Starlark based language that will feel familiar to ytt users. By using a flexible configuration language, Tilt can easily be customized for individual needs and integrated with existing workflows.

Tools you will need to run the demo

• tilt cli
• go for building the demo
• Kubernetes cluster such as kind
• kapp
• ytt
• kbld

Checkout the demo project

First, checkout the project from GitHub

The repository contains a simple Go webserver and a set of manifests for deploying the application to Kubernetes

├── Dockerfile
├── README.md
├── Tiltfile
├── build
│   └── carvel-tilt
├── cmd
│   └── carvel-tilt
│       └── main.go
├── deployments
│   ├── build.yaml
│   ├── deployment.yaml
│   ├── namespace.yaml
│   ├── service.yaml
│   └── values-schema.yml
├── go.mod
├── pkg
│   └── api
│       └── handler.go

Render Kubernetes manifests with ytt

The demo uses ytt to render the Kubernetes YAML, this allows variables such as HTTP port to be substituted at build time. The YAML can be rendered with the command

ytt -f deployments

A number of default values are defined in the file deployments/values-schema.yml, which can be easily overridden. To change the HTTP port of the deployed webserver, use command;

ytt -f deployments --data-value-yaml port=8085

Note, --data-value-yaml is used instead of --data-value because port is an integer value

Building the image with kbld

kbld is used to build the image, this is a very useful tool for local development as it will automatically tag the image and update the Kubernetes manifests. Updating the tag every build is important as it ensures Kubernetes will use the latest image version.

In the demo, kbld uses docker to build the image using the Dockerfile in the root of the project.

Build the image using the following commands.

# Compile the Go binary locally as it will be copied to the Docker image
GOOS=linux GOARCG=amd64 go build -o build/carvel-tilt cmd/carvel-tilt/main.go

# Set REGISTRY variable to an image registry that you access to push images
export REGISTRY=docker.io/my-registry/carvel-tilt-example-go

# Build and push the image
ytt -f deployments -v registry=${REGISTRY} | kbld -f -

The output will show the Kubernetes yaml has been updated to use the tag of freshly built image

Deploy to Kubernetes with kapp

Now we know how to build and tag the image, kapp can deploy the application. kapp builds on the functionality of kubectl apply -f ... by grouping resources and managing dependencies them.

The app can be deployed with the command

     ytt -f deployments -v registry=${REGISTRY}| \
      kbld -f - | \
      kapp deploy -n default -a carvel-tilt-demo -y -f -

Bringing it all together with Tilt

Using Tilt, the ytt, kbld and kapp commands will be automated to run every time a local code change is made. Tilt is configured using the Tiltfile in the root of the project. Visual Studio code has a plugin for editing Tiltfiles and is highly recommended.

Build stage

First, a local_resource is defined to compile the Go application. A local_resource describes a task that runs on the local machine

compile_cmd = """
    rm build/carvel-tilt || true &&
	go build \
        -o build/carvel-tilt \
        cmd/carvel-tilt/main.go &&
        echo "Go build finished\n"
"""
local_resource(
    'go-compile',
    compile_cmd,
    deps=['pkg', 'cmd', 'deployments'],
    env={'GOOS': 'linux', 'GOARCH': 'amd64'}
)

compile_cmd is a variable containing the go build command to run

local_resouce describes how to run the command. The deps argument references the files or folders that will trigger this command to run.

Deploy stage

To deploy the app to Kubernetes, k8s_custom_deploy is defined. This function runs a command that applies Kubernetes resources and then returns the created resources as YAML. kapp inspect is used to return the raw objects for Tilt. The deps argument is set to build/carvel-tilt as this forces Tilt to always run the build stage before the deploy stage.

port = 8084
registry = os.getenv('REGISTRY','docker.io/ojhughes')

kapp_apply_cmd = """
    ytt --file deployments --data-value-yaml port=%d -v registry=%s| 
    kbld -f - | 
    kapp deploy -n default -a carvel-tilt-demo -y -f - > /dev/null &&
    kapp inspect -n default -a carvel-tilt-demo --raw --tty=false
""" % (port, registry)

kapp_delete_cmd = "kapp delete -n default -a carvel-tilt-demo -y"

k8s_custom_deploy(
    name='carvel-tilt-demo',
    deps=['build/carvel-tilt'],
    apply_cmd=kapp_apply_cmd,
    delete_cmd=kapp_delete_cmd
)
k8s_resource('carvel-tilt-demo', port_forwards=port, auto_init=False )

Port forwarding

Tilt can automatically create a port forward for the application using k8s_resource.

k8s_resource(
    'carvel-tilt-demo', 
     port_forwards=port
 )

Running Tilt

Make sure the REGISTRY environment variable is set and simply run tilt up, this will read the Tiltfile and start the build/deploy workflow Once tilt is running, you can press the s key to stream the logs to the console or open http://localhost:10350 in your browser

# Set the variable to a registry you have push access to
export REGISTRY=docker.io/myregistry

# Build and deploy the project
tilt up

# Test the app works using the port forward created by tilt
curl localhost:8084

# Tear everything down
tilt down

You can see the complete Tiltfile here https://github.com/ojhughes/carvel-tilt-example-go/blob/main/Tiltfile

See it in action!