What does Docker pack when you build an image?
A Docker image can carry your app files, the program that runs them and the libraries they need. The Dockerfile is the recipe for making that package. A container is a running instance of the image.
This helps when two machines need the same app setup. Check the destination’s operating system and processor before building. An image built for an ARM Linux target may need another image variant on an x86 Linux host.
Where do bookings go when you replace a container?
Keep bookings in a separate database or on storage set up to survive container replacement. A Docker volume is storage managed separately from the running container. An image does not back up that volume or the database.
Keep the Dockerfile and dependency lock with the code. Save a record of the image version you shipped and a separate backup of the records you need to recover. Keep credentials out of the image. Docker provides temporary secret mounts when a build needs a credential.
When does Docker Desktop need a paid plan?
Docker’s standalone Desktop terms set two thresholds for a commercial organization using it without a paid subscription. It must have fewer than 250 employees and less than US$10 million in annual revenue. Government entities need a paid subscription. Docker also lists free personal, education and noncommercial open-source uses.
Standalone Docker Engine is an open-source project with separate licensing. Check hosting and registry costs separately. A registry such as Docker Hub stores images for people or services to pull, and has its own usage limits.
Can you map what a new host needs on paper?
Draw a fictional workshop booking app with a page, a program that handles reservations and a place where reservations are saved. Do the exercise without opening Docker or connecting a service.
- Separate the recipe from the running copyWrite Dockerfile next to the build instructions. Write image next to the packaged app and its runtime. Write container next to the running copy.
- Keep the sample reservation apartAdd a made-up Tuesday booking to the storage box. If you replace the running copy, mark which storage the new copy must reconnect to.
- Write the destination requirementsChoose a fictional Linux x86 host. Record the matching image target and which backup the host would need to recover the booking. Keep any real project, credentials and image uploads outside this exercise.