Imagine you have a Go application backed up by a database such as PostgreSQL and need to deploy it. In a traditional setup, this can be quite a challenge, but with Juju you’ll find yourself deploying, configuring, scaling, integrating, monitoring, etc., your Go application in no time. Let’s get started!
In this tutorial we will build a rock and Kubernetes charm for a Go application using the charm SDK, so we can have a Go application up and running with Juju in about 90 minutes.
rock
An Ubuntu LTS-based OCI compatible container image designed to meet security, stability, and reliability requirements for cloud-native software.
charm
A package consisting of YAML files + Python code that will automate every aspect of an application’s lifecycle so it can be easily orchestrated with Juju.
Juju
An orchestration engine for software operators that enables the deployment, integration and lifecycle management of applications using charms.
What you’ll need:
- A workstation, e.g., a laptop, with amd64 or arm64 architecture which has sufficient resources to launch a virtual machine with 4 CPUs, 4 GB RAM, and a 50 GB disk
- Familiarity with Linux
What you’ll do:
- Set things up
- Create the Go application
- Run the Go application locally
- Pack the Go application into a rock
- Create the charm
- Deploy the Go application
- Integrate with a database
- Expose the app using ingress
- Clean up environment
Set things up
Install Multipass.
See more: Multipass | How to install Multipass
Use Multipass to launch an Ubuntu VM with the name charm-dev from the 22.04 blueprint:
multipass launch --cpus 4 --disk 50G --memory 4G --name charm-dev 22.04
Once the VM is up, open a shell into it:
multipass shell charm-dev
In order to create the rock, you’ll need to install Rockcraft:
sudo snap install rockcraft --channel latest/edge --classic
LXD will be required for building the rock. Make sure it is installed and initialised:
sudo snap install lxd
lxd init --auto
In order to create the charm, you’ll need to install Charmcraft:
sudo snap install charmcraft --channel latest/edge --classic
MicroK8s is required to deploy the Go application on Kubernetes. Install MicroK8s:
sudo snap install microk8s --channel 1.31-strict/stable
sudo adduser $USER snap_microk8s
newgrp snap_microk8s
Wait for MicroK8s to be ready using sudo microk8s status --wait-ready. Several MicroK8s add-ons are required for deployment:
sudo microk8s enable hostpath-storage
# Required to host the OCI image of the Go application
sudo microk8s enable registry
# Required to expose the Go application
sudo microk8s enable ingress
See more: ingress^
Juju is required to deploy the Go application. Install Juju and bootstrap a development controller:
sudo snap install juju --channel 3.5/stable
mkdir -p ~/.local/share
juju bootstrap microk8s dev-controller
Finally, create a new directory for this tutorial and go inside it:
mkdir go-hello-world
cd go-hello-world
This tutorial requires version 3.2.0 or later of Charmcraft. Check the version of Charmcraft using charmcraft --version If you have an older version of Charmcraft installed, use sudo snap refresh charmcraft --channel latest/edge to get the latest edge version of Charmcraft.
This tutorial requires version 1.5.4 or later of Rockcraft. Check the version of Rockcraft using rockcraft --version If you have an older version of Rockcraft installed, use sudo snap refresh rockcraft --channel latest/edge to get the latest edge version of Rockcraft.
Create the Go application
Start by creating the “Hello, world” Go application that will be used for this tutorial.
Install go and initialise the Go module:
sudo snap install go --classic
go mod init go-hello-world
Create a main.go file, copy the following text into it and then save it:
package main
import (
"fmt"
"log"
"net/http"
)
func helloWorldHandler(w http.ResponseWriter, req *http.Request) {
log.Printf("new hello world request")
fmt.Fprintln(w, "Hello, world!")
}
func main() {
log.Printf("starting hello world application")
http.HandleFunc("/", helloWorldHandler)
http.ListenAndServe(":8080", nil)
}
Run the Go application locally
Build the Go application so it can be run:
go build .
Now that we have a binary compiled, let’s run the Go application to verify that it works:
./go-hello-world
Test the Go application by using curl to send a request to the root endpoint. You may need a new terminal for this; if you are using Multipass use multipass shell charm-dev to get another terminal:
curl localhost:8080
The Go application should respond with Hello, world!. The Go application looks good, so we can stop for now using ctrl + c.
Pack the Go application into a rock
First, we’ll need a rockcraft.yaml file. Rockcraft will automate its creation and tailoring for a Go application by using the go-framework profile:
rockcraft init --profile go-framework
The rockcraft.yaml file will automatically be created and set the
name based on your working directory. Open the file in a text editor
and check that the name is go-hello-world. Ensure that platforms
includes the architecture of your host. For example, if your host uses
the ARM architecture, include arm64 in platforms.
For this tutorial, we’ll use the name “go-hello-world” and assume you are on the amd64 platform. Check the architecture of your system using dpkg --print-architecture. Choosing a different name or running on a different platform will influence the names of the files generated by Rockcraft.
Pack the rock:
ROCKCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true rockcraft pack
Depending on your system and network, this step can take a couple of minutes to finish.
Once Rockcraft has finished packing the Go rock, you’ll find a new file in your working directory with the .rock extension:
ls *.rock -l
If you changed the name or version in rockcraft.yaml or are not on an amd64 platform, the name of the .rock file will be different for you.
The rock needs to be copied to the Microk8s registry so that it can be deployed in the Kubernetes cluster:
rockcraft.skopeo --insecure-policy copy --dest-tls-verify=false \
oci-archive:go-hello-world_0.1_amd64.rock \
docker://localhost:32000/go-hello-world:0.1
See more: skopeo^
Create the charm
Create a new directory for the charm and go inside it:
mkdir charm
cd charm
We’ll need a charmcraft.yaml, requirements.txt and source code for the charm. The source code contains the logic required to operate the Go application. Charmcraft will automate the creation of these files by using the go-framework profile:
charmcraft init --profile go-framework --name go-hello-world
The files will automatically be created in your working directory.
The charm depends on several libraries. Download the libraries and pack the charm:
CHARMCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true charmcraft fetch-libs
CHARMCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true charmcraft pack
Depending on your system and network, this step can take a couple of minutes to finish.
Once Charmcraft has finished packing the charm, you’ll find a new file in your working directory with the .charm extension:
ls *.charm -l
If you changed the name in charmcraft.yaml or are not on the amd64 platform, the name of the .charm file will be different for you.
Deploy the Go application
A Juju model is needed to deploy the application. Let’s create a new model:
juju add-model go-hello-world
If you are not on a host with the amd64 architecture, you will need to include a constraint to the Juju model to specify your architecture. For example, for the arm64 architecture, use juju set-model-constraints -m go-hello-world arch=arm64. Check the architecture of your system using dpkg --print-architecture.
Now the Go application can be deployed using Juju:
juju deploy ./go-hello-world_amd64.charm \
go-hello-world \
--resource app-image=localhost:32000/go-hello-world:0.1
It will take a few minutes to deploy the Go application. You can monitor the progress using juju status --watch 5s. Once the status of the App has gone to active, you can stop watching using ctrl + c.
See more: Command ‘juju status’
The Go application should now be running. We can monitor the status of the deployment using juju status which should be similar to the following output:
go-hello-world microk8s microk8s/localhost 3.5.4 unsupported 14:35:07+02:00
App Version Status Scale Charm Channel Rev Address Exposed Message
go-hello-world active 1 go-hello-world 0 10.152.183.229 no
Unit Workload Agent Address Ports Message
go-hello-world/0* active idle 10.1.157.79
The deployment is finished when the status shows active. Let’s expose the application using ingress. Deploy the nginx-ingress-integrator charm and integrate it with the Go app:
juju deploy nginx-ingress-integrator --trust
juju integrate nginx-ingress-integrator go-hello-world
The hostname of the app needs to be defined so that it is accessible via the ingress. We will also set the default route to be the root endpoint:
juju config nginx-ingress-integrator \
service-hostname=go-hello-world path-routes=/
By default, the port for the Go application should be 8080. If you want to change the default port, it can be done
with the configuration option app-port that will be exposed as APP_PORT to the Go application.
Monitor juju status until everything has a status of active. Use curl http://go-hello-world --resolve go-hello-world:80:127.0.0.1 to send a request via the ingress. The Go application should respond with Hello, world!.
Configure the Go application
Now let’s customise the greeting using a configuration option. We will expect this configuration option to be available in the Go app configuration under the keyword GREETING. Go back out to the root directory of the project using cd .. and copy the following code into main.go:
package main
import (
"fmt"
"log"
"os"
"net/http"
)
func helloWorldHandler(w http.ResponseWriter, req *http.Request) {
log.Printf("new hello world request")
greeting, found := os.LookupEnv("APP_GREETING")
if !found {
greeting = "Hello, world!"
}
fmt.Fprintln(w, greeting)
}
func main() {
log.Printf("starting hello world application")
http.HandleFunc("/", helloWorldHandler)
http.ListenAndServe(":8080", nil)
}
Open rockcraft.yaml and update the version to 0.2. Run ROCKCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true rockcraft pack again, then upload the new OCI image to the MicroK8s registry:
rockcraft.skopeo --insecure-policy copy --dest-tls-verify=false \
oci-archive:go-hello-world_0.2_amd64.rock \
docker://localhost:32000/go-hello-world:0.2
Change back into the charm directory using cd charm. The go-framework Charmcraft extension supports adding configurations to charmcraft.yaml which will be passed as environment variables to the Go application. Add the following to the end of the charmcraft.yaml file:
config:
options:
greeting:
description: |
The greeting to be returned by the Go application.
default: "Hello, world!"
type: string
Configuration options are automatically capitalised and - are replaced by _. A APP_ prefix will also be added.
Run CHARMCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true charmcraft pack again. The deployment can now be refreshed to make use of the new code:
juju refresh go-hello-world \
--path=./go-hello-world_amd64.charm \
--resource app-image=localhost:32000/go-hello-world:0.2
Wait for juju status to show that the App is active again. Verify that the new configuration has been added using juju config go-hello-world | grep -A 6 greeting: which should show the configuration option.
The grep command extracts a portion of the configuration to make it easier to check whether the configuration option has been added.
Using curl http://go-hello-world --resolve go-hello-world:80:127.0.0.1 shows that the response is still Hello, world! as expected. The greeting can be changed using Juju:
juju config go-hello-world greeting='Hi!'
curl http://go-hello-world --resolve go-hello-world:80:127.0.0.1 now returns the updated Hi! greeting.
It might take a short time for the configuration to take effect.
Integrate with a database
Now let’s keep track of how many visitors your application has received. This will require integration with a database to keep the visitor count. This will require a few changes:
- We will need to create a database migration that creates the
visitorstable - We will need to keep track how many times the root endpoint has been called in the database
- We will need to add a new endpoint to retrieve the number of visitors from the database
The charm created by the go-framework extension will execute the migrate.sh script if it exists. This script should ensure that the database is initialised and ready to be used by the application. We will create a migrate.sh file containing this logic.
Go back out to the tutorial root directory using cd ... Create the migrate.sh file using a text editor and paste the following code into it:
#!/bin/bash
PGPASSWORD="${POSTGRESQL_DB_PASSWORD}" psql -h "${POSTGRESQL_DB_HOSTNAME}" -U "${POSTGRESQL_DB_USERNAME}" "${POSTGRESQL_DB_NAME}" -c "CREATE TABLE IF NOT EXISTS visitors (timestamp TIMESTAMP NOT NULL, user_agent TEXT NOT NULL);"
The charm will pass the Database connection string in the POSTGRESQL_DB_CONNECT_STRING environment variable once PostgreSQL has been integrated with the charm.
Change the permissions of the file migrate.sh so it is executable:
chmod u+x migrate.sh
For the migrations to work we need the postgresql-client package
installed in the rock. As by default the go-framework uses the base
base, we would also need to install a shell interpreter. Let’s do it
as a slice, so the rock does not include unnecessary files. Open the rockcraft.yaml file using a text editor, update the version to 0.3 and add the
following to the end:
parts:
runtime-debs:
plugin: nil
stage-packages:
# Added manually for the migrations
- postgresql-client
runtime-slices:
plugin: nil
stage-packages:
# Added manually for the migrations
- bash_bins
To be able to connect to PostgreSQL from the Go app the library pgx will be used.
The app code needs to be updated to keep
track of the number of visitors and to include a new endpoint to
retrieve the number of visitors to the app. Open main.go in a text
editor and replace its contents with the following code:
package main
import (
"database/sql"
"fmt"
"log"
"net/http"
"os"
"time"
_ "github.com/jackc/pgx/v5/stdlib"
)
func helloWorldHandler(w http.ResponseWriter, req *http.Request) {
log.Printf("new hello world request")
postgresqlURL := os.Getenv("POSTGRESQL_DB_CONNECT_STRING")
db, err := sql.Open("pgx", postgresqlURL)
if err != nil {
log.Printf("An error occurred while connecting to postgresql: %v", err)
return
}
defer db.Close()
ua := req.Header.Get("User-Agent")
timestamp := time.Now()
_, err = db.Exec("INSERT into visitors (timestamp, user_agent) VALUES ($1, $2)", timestamp, ua)
if err != nil {
log.Printf("An error occurred while executing query: %v", err)
return
}
greeting, found := os.LookupEnv("APP_GREETING")
if !found {
greeting = "Hello, world!"
}
fmt.Fprintln(w, greeting)
}
func visitorsHandler(w http.ResponseWriter, req *http.Request) {
log.Printf("visitors request")
postgresqlURL := os.Getenv("POSTGRESQL_DB_CONNECT_STRING")
db, err := sql.Open("pgx", postgresqlURL)
if err != nil {
return
}
defer db.Close()
var numVisitors int
err = db.QueryRow("SELECT count(*) from visitors").Scan(&numVisitors)
if err != nil {
log.Printf("An error occurred while executing query: %v", err)
return
}
fmt.Fprintf(w, "Number of visitors %d\n", numVisitors)
}
func main() {
log.Printf("starting hello world application")
http.HandleFunc("/", helloWorldHandler)
http.HandleFunc("/visitors", visitorsHandler)
http.ListenAndServe(":8080", nil)
}
Check all the packages and their dependencies in the Go project with the following command:
go mod tidy
Run ROCKCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true rockcraft pack and upload the newly created rock to the MicroK8s registry:
rockcraft.skopeo --insecure-policy copy --dest-tls-verify=false \
oci-archive:go-hello-world_0.3_amd64.rock \
docker://localhost:32000/go-hello-world:0.3
Go back into the charm directory using cd charm. The Go app now requires a database which needs to be declared in the charmcraft.yaml file. Open charmcraft.yaml in a text editor and add the following section to the end:
requires:
postgresql:
interface: postgresql_client
optional: false
Pack the charm using CHARMCRAFT_ENABLE_EXPERIMENTAL_EXTENSIONS=true charmcraft pack and refresh the deployment using Juju:
juju refresh go-hello-world \
--path=./go-hello-world_amd64.charm \
--resource app-image=localhost:32000/go-hello-world:0.3
Deploy postgresql-k8s using Juju and integrate it with go-hello-world:
juju deploy postgresql-k8s --trust
juju integrate go-hello-world postgresql-k8s
Wait for juju status to show that the App is active again. curl http://go-hello-world --resolve go-hello-world:80:127.0.0.1 should still return the Hi! greeting. To check the total visitors, use curl http://go-hello-world/visitors --resolve go-hello-world:80:127.0.0.1 which should return Number of visitors 1 after the previous request to the root endpoint and should be incremented each time the root endpoint is requested. If we perform another request to curl http://go-hello-world --resolve go-hello-world:80:127.0.0.1, curl http://go-hello-world/visitors --resolve go-hello-world:80:127.0.0.1 will return Number of visitors 2.
Clean up environment
We’ve reached the end of this tutorial. We have created a Go application, deployed it locally, integrated it with a database and exposed it via ingress!
If you’d like to reset your working environment, you can run the following in the root directory for the tutorial:
cd ..
rm -rf charm
# delete all the files created during the tutorial
rm go-hello-world_0.1_amd64.rock go-hello-world_0.2_amd64.rock \
go-hello-world_0.3_amd64.rock rockcraft.yaml main.go \
migrate.sh go-hello-world go.mod go.sum
# Remove the juju model
juju destroy-model go-hello-world --destroy-storage
If you created an instance using Multipass, you can also clean it up. Start by exiting it:
exit
And then you can proceed with its deletion:
multipass delete charm-dev
multipass purge
Next steps
| If you are wondering… | visit… |
|---|---|
| “How do I…?” | SDK How-to docs |
| “How do I debug?” | Charm debugging tools |
| “What is…?” | SDK Reference docs |
| “Why…?”, “So what?” | SDK Explanation docs |
Contributors: @econley, @jdkandersson , @javierdelapuente