To run the Flask API inside of a container, the Docker image must exist inside of Azure Container Registry

To build the Docker image

docker build -t name_of_docker_image_tag .

To create the Azuure Container Registry

az acr create --name name_of_acr --resource-group name_of_rg --sku Standard

To log into the ACR from the terminal

az acr login --name name_of_acr

To tag and push the Docker image and prepare it for a push to ACR

docker tag name_of_docker_image_tag name_of_acr.azurecr.io/azureapi/flask docker push name_of_acr.azurecr.io/azureapi/flask