Creating components using odo

Component is the most basic unit of operation for odo. And the way to create one is using odo create (short for odo component create) command.

In simplest terms, when you "create" an odo component, you populate your current working directory with the file devfile.yaml. A Devfile is a manifest file that contains information about various resources (URL, Storage, Services, etc.) that correspond to your component, and will be created on the Kubernetes cluster when you execute odo push command. Most odo commands will first modify (add or remove configuration from) this file, and then subsequent odo push will create or delete the resources from the Kubernetes cluster.

However, odo users are not expected to know how the devfile.yaml is organized; it is the odo commands that would create, update, or delete it.

One final thing to keep in mind - there can be only one odo component in a directory. Nesting odo components is not expected to work well. In other terms, if you have multiple parts (components), say frontend and backend, of your microservices application that you want to create odo components for, you should put them in separate directories and not try to nest them. Take a look at example structure below:

$ tree my-awesome-microservices-app 
my-awesome-microservices-app
├── backend
│   └── devfile.yaml
└── frontend
    └── devfile.yaml

In this guide, we are going to create a Spring Boot component and a Nodejs component to deploy parts of the odo quickstart project to a Kubernetes cluster.

Let's clone the project first:

git clone https://github.com/dharmit/odo-quickstart
cd odo-quickstart

Next, create a project on the Kubernetes cluster in which we will be creating our component. This is to keep our Kubernetes cluster clean of the tasks we perform (this step is optional):

odo project create myproject

Alternatively, you could also use one of the existing projects on the cluster:

odo project list

Now, set the project in which you want to create the component:

# replace <project-name> with a valid value from the list
odo project set <project-name>

odo supports interactive and non-interactive ways of creating a component. We will create the Spring Boot component interactively and Nodejs component non-interactively. The Spring Boot component is in backend directory. It contains code for the REST API that our Nodejs component will be interacting with. This Nodejs component is in frontend directory.

Creating a component interactively

To interactively create the Spring Boot component, cd into the cloned project (already done if you copy-pasted the command above), then cd into backend directory, and execute:

cd backend
odo create

You will be prompted with a few questions one after the another. Go through each one of them to create a component.

1. First question is about selecting the component type:

   $ odo create
   ? Which devfile component type do you wish to create  [Use arrows to move, enter to select, type to filter]
   > java-maven
   java-maven
   java-openliberty
   java-openliberty
   java-quarkus
   java-quarkus
   java-springboot

   By default, java-maven is selected for us. Since this is a Spring Boot application, we should be selecting java-springboot.

   We can either scroll down to java-springboot using the arrow key, or start typing spring on the prompt. Typing spring will lead to odo filtering the component type based on your input.

2. Next, odo asks you to name the component:

   $ odo create                
   ? Which devfile component type do you wish to create java-springboot
   ? What do you wish to name the new devfile component (java-springboot) backend

   Name it backend.

3. Next, odo asks you for the project in which you would like to create the component. Use the project myproject that we created earlier or the one you had set using odo project set command

   $ odo create
   ? Which devfile component type do you wish to create java-springboot
   ? What do you wish to name the new devfile component java-springboot
   ? What project do you want the devfile component to be created in myproject

   Now you will have a devfile.yaml in your current working directory. But odo is not done asking you questions yet.

4. Lastly, odo asks you if you would like to download a "starter project". Since we already cloned the odo-quickstart project, we answer in No by typing n and hitting the return key. We discuss starter projects later in this document:

   $ odo create
   ? Which devfile component type do you wish to create java-springboot
   ? What do you wish to name the new devfile component java-springboot
   ? What project do you want the devfile component to be created in myproject
   Devfile Object Validation
   ✓  Checking devfile existence [66186ns]
   ✓  Creating a devfile component from registry: stage [92202ns]
   Validation
   ✓  Validating if devfile name is correct [99609ns]
   ? Do you want to download a starter project (y/N) n

Your Spring Boot component is now ready for use.

Creating a component non-interactively

To non-interactively create the Nodejs component to deploy our frontend code, cd into the cloned frontend directory and execute:

# assuming you are in the odo-quickstart/backend directory
cd ../frontend 
odo create nodejs frontend -n myproject

Here nodejs is the type of the component, frontend is the name of the component, and -n myproject tells odo to use the project myproject for the mentioned odo create operation.

Starter projects

Besides creating a component for an existing code, you could also use "starter project" when creating a component.

Starter projects are example projects developed by the community to showcase the usability of devfiles. An odo user can use these starter projects by running odo create command in an empty directory.

Starter projects in interactive mode

To interactively create a Java Spring Boot component using the starter project, you can follow the below steps:

mkdir myOdoComponent && cd myOdoComponent
odo create

In the questions that odo asks you next, provide answers like below:

$ odo create
? Which devfile component type do you wish to create java-springboot
? What do you wish to name the new devfile component myFirstComponent
? What project do you want the devfile component to be created in myproject
Devfile Object Validation
 ✓  Checking devfile existence [60122ns]
 ✓  Creating a devfile component from registry: stage [91411ns]
Validation
 ✓  Validating if devfile name is correct [35749ns]
? Do you want to download a starter project Yes

Starter Project
 ✓  Downloading starter project springbootproject from https://github.com/odo-devfiles/springboot-ex.git [716ms]

Please use `odo push` command to create the component with source deployed

Starter projects in non-interactive mode

To non-interactively create a Java Spring Boot component using the starter project, you can follow the below steps:

mkdir myOdoComponent && cd myOdoComponent
odo create java-springboot myFirstComponent --starter springbootproject

Push the component to Kubernetes

odo follows a "create & push" workflow for almost all the commands. Meaning, most odo commands won't create resources on Kubernetes cluster unless you run odo push command.

Among the various ways described above, irrespective of how you created the component, the next step to create the resources for our component on the cluster would be to run odo push.

Execute below command from the component directory of both the frontend and backend components:

odo push