EBS Volume Detach throws 500

[AnirudhNarsipur]

Trying to detach an EBS volume throws a 500. LocalStack logs show:

2026-06-25T01:59:18.485 ERROR --- [et.reactor-2] l.aws.handlers.logging     : exception during call chain: object of type 'NoneType' has no len()
2026-06-25T01:59:18.486  INFO --- [et.reactor-2] localstack.request.aws     : AWS ec2.DetachVolume => 500 (InternalError)

Full repro script attached. Output from running repro script:

> bash repro_detach_volume_bug.sh
LocalStack CLI: LocalStack CLI 2026.6.0
AWS CLI: aws-cli/2.33.2 Python/3.13.11 Darwin/25.4.0 exe/arm64
endpoint: http://localhost:4566
region: us-west-2
availability zone: us-west-2a
starting LocalStack

     __                     _______ __             __
    / /   ____  _________ _/ / ___// /_____ ______/ /__
   / /   / __ \/ ___/ __ `/ /\__ \/ __/ __ `/ ___/ //_/
  / /___/ /_/ / /__/ /_/ / /___/ / /_/ /_/ / /__/ ,<
 /_____/\____/\___/\__,_/_//____/\__/\__,_/\___/_/|_|

- LocalStack CLI: 2026.6.0
- Profile: default
- App: https://app.localstack.cloud

[19:18:36] starting LocalStack in Docker mode 🐳                                                                localstack.py:172
2026-06-24T19:18:36.934  INFO --- [  MainThread] l.p.c.b.licensingv2        : Successfully activated cached license <redacted_license_id>:trial from /Users/latch/Library/Caches/localstack-cli/license.json 🔑✅
           preparing environment                                                                                 bootstrap.py:437
[19:18:37] configuring container                                                                                 bootstrap.py:440
           starting container                                                                                    bootstrap.py:440
           detaching                                                                                             bootstrap.py:440
waiting for LocalStack
curl: (52) Empty reply from server
curl: (52) Empty reply from server
curl: (52) Empty reply from server
curl: (52) Empty reply from server
curl: (52) Empty reply from server
resetting all LocalStack state at http://localhost:4566
creating EC2 resources
waiting for instance to run
waiting for volume to become available
{
    "VolumeId": "vol-512248300002efbe4",
    "InstanceId": "i-2d95601b9ff975a1c",
    "Device": "/dev/sdf",
    "State": "attaching",
    "AttachTime": "2026-06-25T02:18:49+00:00"
}
waiting for volume to become in-use
created:
  vpc: vpc-f16ed8c37fd2a1c63
  subnet: subnet-22dd93d6fd7a454f4
  image: ami-a8808e3b
  instance: i-2d95601b9ff975a1c
  volume: vol-512248300002efbe4
  device: /dev/sdf
volume before detach:
{
    "Volumes": [
        {
            "Iops": 3000,
            "VolumeType": "gp3",
            "VolumeId": "vol-512248300002efbe4",
            "Size": 8,
            "SnapshotId": "",
            "State": "in-use",
            "CreateTime": "2026-06-25T02:18:48+00:00",
            "Attachments": [
                {
                    "DeleteOnTermination": false,
                    "VolumeId": "vol-512248300002efbe4",
                    "InstanceId": "i-2d95601b9ff975a1c",
                    "Device": "/dev/sdf",
                    "State": "attached",
                    "AttachTime": "2026-06-25T02:18:49+00:00"
                }
            ],
            "Encrypted": false
        }
    ]
}
calling DetachVolume with VolumeId only

An error occurred (InternalError) when calling the DetachVolume operation (reached max retries: 2): exception while calling ec2.DetachVolume: object of type 'NoneType' has no len()
reproduced LocalStack DetachVolume error

Script:

#!/usr/bin/env bash
set -euo pipefail

endpoint="http://localhost:4566"
region="us-west-2"
az="us-west-2a"

aws_local() {
  aws --endpoint-url "${endpoint}" --region "${region}" --no-sign-request "$@"
}

wait_for_localstack() {
  for _ in $(seq 1 90); do
    if curl -fsS "${endpoint}/_localstack/health" >/dev/null; then
      return 0
    fi

    sleep 1
  done

  echo "LocalStack did not become healthy at ${endpoint}" >&2
  return 1
}

echo "LocalStack CLI: $(localstack --version)"
echo "AWS CLI: $(aws --version)"
echo "endpoint: ${endpoint}"
echo "region: ${region}"
echo "availability zone: ${az}"

echo "starting LocalStack"
localstack start -d

echo "waiting for LocalStack"
wait_for_localstack

echo "resetting all LocalStack state at ${endpoint}"
curl -fsS --request POST "${endpoint}/_localstack/state/reset" >/dev/null

echo "creating EC2 resources"
vpc_id="$(
  aws_local ec2 create-vpc \
    --cidr-block 10.0.0.0/16 \
    --query 'Vpc.VpcId' \
    --output text
)"

subnet_id="$(
  aws_local ec2 create-subnet \
    --vpc-id "${vpc_id}" \
    --cidr-block 10.0.1.0/24 \
    --availability-zone "${az}" \
    --query 'Subnet.SubnetId' \
    --output text
)"

image_id="$(
  aws_local ec2 register-image \
    --name "detach-volume-repro-$(date +%s)" \
    --description "Minimal DetachVolume repro" \
    --architecture x86_64 \
    --root-device-name /dev/xvda \
    --virtualization-type hvm \
    --block-device-mappings '[{"DeviceName":"/dev/xvda","Ebs":{"VolumeSize":8,"DeleteOnTermination":true,"VolumeType":"gp3"}}]' \
    --query 'ImageId' \
    --output text
)"

instance_id="$(
  aws_local ec2 run-instances \
    --image-id "${image_id}" \
    --instance-type t3.small \
    --subnet-id "${subnet_id}" \
    --count 1 \
    --query 'Instances[0].InstanceId' \
    --output text
)"

echo "waiting for instance to run"
aws_local ec2 wait instance-running --instance-ids "${instance_id}"

volume_id="$(
  aws_local ec2 create-volume \
    --availability-zone "${az}" \
    --size 8 \
    --volume-type gp3 \
    --query 'VolumeId' \
    --output text
)"

echo "waiting for volume to become available"
aws_local ec2 wait volume-available --volume-ids "${volume_id}"

device="/dev/sdf"
aws_local ec2 attach-volume \
  --volume-id "${volume_id}" \
  --instance-id "${instance_id}" \
  --device "${device}" \
  --output json

echo "waiting for volume to become in-use"
aws_local ec2 wait volume-in-use --volume-ids "${volume_id}"

echo "created:"
echo "  vpc: ${vpc_id}"
echo "  subnet: ${subnet_id}"
echo "  image: ${image_id}"
echo "  instance: ${instance_id}"
echo "  volume: ${volume_id}"
echo "  device: ${device}"

echo "volume before detach:"
aws_local ec2 describe-volumes --volume-ids "${volume_id}" --output json

# DetachVolume only requires VolumeId for a normal single-attach EBS volume.
echo "calling DetachVolume with VolumeId only"
set +e
detach_output="$(aws_local ec2 detach-volume --volume-id "${volume_id}" --output json 2>&1)"
detach_status="$?"
set -e

printf '%s\n' "${detach_output}"

if [[ "${detach_status}" -eq 0 ]]; then
  echo "DetachVolume succeeded; bug did not reproduce"
  exit 1
fi

if grep -Fq "object of type 'NoneType' has no len()" <<<"${detach_output}"; then
  echo "reproduced LocalStack DetachVolume error"
  exit 0
fi

echo "DetachVolume failed with a different error" >&2
exit "${detach_status}"

note: Repro script was authored by Codex.