how does nodejs docker kubernetes and travis work for process.env.Foo

Disclaimer: this is a project work.
I might be having issues with the follow but here is what I am doing:

push changes to github
travils builds image and pushes to docker
AWS EKS pulls the image and starts container

now my issue is the following variable is undefined:

         const = process.env.FOO

i am really lost on how to set FOO. I already tried setting it in deployment.yaml, travis.yml and Dockerfile (ENV foo=bar). I have seen documentations with docker-compose but is there a way without docker-compose?