Uploads involve authorization, transfer, metadata and post-processing. A completed transfer does not necessarily mean the content is ready to publish.
Before you start
You should understand API requests, storage and basic capacity estimates. Begin with a concrete user action and its correctness requirement. Draw data flow and failure boundaries before selecting infrastructure; a technology name by itself does not explain why a design meets the requirement.
The practical goal is to reason through this situation: An upload receives a controlled destination, then validation marks the object usable. Read the walkthrough first, then try the interview exercise before opening its answer. The important part is explaining the decision and its consequences, rather than remembering a definition alone.
Step-by-step walkthrough
Step 1: Authorize the destination
A client may upload only to its intended object scope.
Step 2: Separate transfer and readiness
Completed bytes can still fail validation or processing.
Step 3: Verify completion
Confirm ownership, size and required checks before publishing metadata.
Worked scenario
An upload receives a controlled destination, then validation marks the object usable.
An image reaches object storage, but decoding reveals invalid content. Marking it public from a client-reported success would expose unusable or unsafe material. Keep the object pending until the server’s completion workflow verifies its contract, then publish a ready status linked to that exact object.
Common mistake
Trusting client-reported completion can expose incomplete or invalid data.
Verify the behavior
Test partial upload, duplicate completion and failed validation.
Interview exercise
Design a completion step.
Answer and reasoning
Verify object ownership, size and expected processing state before publishing metadata or granting access.
Continue learning
Compare the scenario with the System Design interview questions and test your understanding with the System Design MCQs. For terminology and implementation details, consult the reference material.