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What is the issue with this Docker service update command for canary deployment?

medium📝 Troubleshoot Q6 of 15
Docker - Production Patterns

What is the issue with this Docker service update command for canary deployment?

docker service update --image myapp:v2 --update-parallelism -1 myservice

A--update-parallelism must be zero to update all containers at once
BThe image tag 'v2' is invalid
CThe service name 'myservice' is missing
D--update-parallelism cannot be negative
Step-by-Step Solution
Solution:

  1. Step 1: Analyze the command

    The flag --update-parallelism controls how many containers update simultaneously and must be a positive integer.

  2. Step 2: Identify the error

    Using -1 is invalid because parallelism cannot be negative.

  3. Final Answer:

    --update-parallelism cannot be negative -> Option D

  4. Quick Check:

    Parallelism must be positive integer [OK]
Quick Trick: Parallelism value must be positive integer [OK]
Common Mistakes:
  • Using negative values for --update-parallelism
  • Confusing image tag errors with update flags
  • Omitting service name in the command

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