How to create Deployment on nginx with custom text in index.html?

here you are using the build-in docker image for nginx. and you can't produce custom html as you are using the pre-build docker image. even you can't change anything in nginx server. as this one is already build in docker and k8s is just pulling that image from docker and run it.

To create custom index.hmtl with a text "welcome to the lab", you need to build your own docker image and then by using that image you can create the kubernetes deployment.

containers:      - name: nginx        image: nginx        ports:        - containerPort: 80

here, in the manifest you are giving the specification of the container, where you used nginx image and you can not change the image as you have no access of the dockerfile by which that image were created.

In your deployment manifest you give two specification, in outer specification you give the replicas which means how many replica of your application need to run. Another specification is the container specification, here you give your application image which can be your own image or others image like nginx, now the when the deployment create successfully and also the pods then you will only see the things that was defined in your used application image. So, you if you want different things than you need different image containing your desired outputs.