Workshop Exercise 2.2 - Deploying the PLC Application

Table of Contents

• Objective
• Step 1 - What are initContainers
• Step 2 - Update the template

Objective

• Understand the concept of InitContainers
• Update our HELM chart to download the PLC application

Step 1 - What are initContainers

Getting additional binary data into a container can be somewhat daunting for those not used to the microservices method of working.

For this scenario, since our PLC controller is a generic image, this makes it handy to deploy multiple different applications and just template out the application parts.

For this exercise, let us use a kubernetes tool called initCOntainers. These are special containers that can be used to do avariety of tasks before starting our main application container in the deployment. For instance, in our case we want to copy the needed application file into the correct directory within our PLC’s storage directory. You could also use it to ping a dependent service or verify if prerequisits are available, or just delaying startup by some bit for whatever reason necessary.

For more information, feel free to check out the docs

Step 2 - Update the template

Let’s start of by retrieving a pre-compiled application for the PLC. We have generated one which can be downloaded from this repo You can click on the file and select the “download raw file” option

Download both the app and crc files and upload to your team’s gitea repo. In practice, the commit to the repo should be the last step of the build process when publishing new application logic.

Let’s create a location within your gitea. In this example a new repository was added specifically for the binaries.

Once uploaded, remember to commit changes.

We will need to update our templates in order to get these files into the PLC container.

Let’s start by adding the new URLs to our values.yaml file. For simplicity’s sake, we’ll add the same one to both. Edit the existing values.yaml and update it with the new entries.

---
plcs:
  - name: codesys-plc-1
    appUrl: https://github.com/redhat-manufacturing/device-edge-workshops/blob/c31081a2c697d17e9891f1ff3f17ed9457d6b90c/exercises/acp_existing_nextgen/codesys/2.1-deploying-plc-application/application/
    partOf: codesys
    appName: Application
    serialNo: 00000000333a536a
  - name: another-plc
    appUrl: https://github.com/redhat-manufacturing/device-edge-workshops/blob/c31081a2c697d17e9891f1ff3f17ed9457d6b90c/exercises/acp_existing_nextgen/codesys/2.1-deploying-plc-application/application/
    partOf: codesys
    appName: Application
    serialNo: 00000000333a536b

With these values and the files available, we can continue to add them to our deployment template before hitting the sync button in argoCD Edit the templates/deployment.yaml file and add the initContainer section

...
containers:
...
initContainers:
  - name: init-plc-application
    image: ubi9/ubi-minimal
    command: ['sh', '-c', "mkdir -p /data/codesyscontrol/PlcLogic/Application && cd /data/codesyscontrol/PlcLogic/Application && curl -O {{ .appUrl }}/Application.app && curl -O {{ .appUrl }}/Application.crc" ]
    volumeMounts:
      - mountPath: "/data/codesyscontrol"
        name: data-storage 
...

---

Navigation

Previous Exercise

Next Exercise

Click here to return to the Workshop Homepage