resize-instance.sh

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Purpose

Safely resize an EC2 instance type using controlled stop-modify-start workflow.

Location

cloud/aws/ec2/resize-instance.sh

Preconditions

  • Required tools: bash, aws, date, sleep
  • Required permissions: ec2:DescribeInstances, ec2:StopInstances, ec2:ModifyInstanceAttribute, ec2:StartInstances
  • Required environment variables: none

Arguments

Flag Required Default Description
--id INSTANCE_ID Yes N/A Target instance ID
--instance-type TYPE Yes N/A Destination instance type (e.g. m6i.large)
--region REGION No AWS CLI default AWS region override
--profile PROFILE No AWS CLI default AWS profile override
--allow-stop No false Required to resize running instances
--start-after No auto Force start after resize
--no-start-after No auto Keep stopped after resize
--wait No true Wait for state transitions
--no-wait No false Do not wait for state transitions
--timeout SEC No 1200 Wait timeout
--poll-interval SEC No 15 Poll interval
--dry-run No false Print commands only

Scenarios

  • Happy path: running instance is stopped, resized, restarted, and returns to running.
  • Common operational path: scheduled right-sizing with explicit approval to stop workloads.
  • Failure path: running instance without --allow-stop, invalid type, or blocked modify call.
  • Recovery/rollback path: revert to previous type and restart using same workflow if needed.

Usage

cloud/aws/ec2/resize-instance.sh --id i-0123456789abcdef0 --instance-type m6i.large --allow-stop
cloud/aws/ec2/resize-instance.sh --id i-0123456789abcdef0 --instance-type c7i.xlarge --allow-stop --no-start-after
cloud/aws/ec2/resize-instance.sh --id i-0123456789abcdef0 --instance-type m6i.large --dry-run

Behavior

  • Main execution flow:
  • validates instance/type inputs and current state
  • enforces explicit stop permission for running instances
  • stops instance if needed, modifies instance type, then optionally restarts
  • waits for state transitions when enabled
  • Idempotency notes: no-op if current type already matches target.
  • Side effects: planned instance downtime and compute shape change.

Output

  • Standard output format: timestamped lifecycle logs on stderr.
  • Exit codes:
  • 0 success
  • 2 invalid arguments/precondition failures
  • non-zero AWS/API/wait failures

Failure Modes

  • Common errors and likely causes:
  • unsupported/invalid target type for region or architecture
  • modify permission denied
  • timeout on stop/start transition
  • Recovery and rollback steps:
  • validate type availability and IAM scope
  • rerun with previous type if rollback is required
  • inspect EC2 instance events for transition blockers

Security Notes

  • Secret handling: none.
  • Least-privilege requirements: limit modify/start/stop permissions to approved instance scopes.
  • Audit/logging expectations: resizing actions should map to capacity and change-management approvals.

Testing

  • Unit tests:
  • argument/precondition validation
  • start-after mode selection logic
  • Integration tests:
  • resize workflow for stopped and running instances
  • Manual verification:
  • confirm InstanceType change and final State.Name
reboot-instance.sh tag-instance.sh