az vm create fails with "ERROR: Extra data: line 1 column 4 (char 3)" across multiple Azure CLI versions

Question

az vm create fails with "ERROR: Extra data: line 1 column 4 (char 3)" across multiple Azure CLI versions

Koteru Reddy (LTIMindtree Limited) 85 Microsoft External Staff

We are seeing consistent provisioning failures when running az vm create, returning the following error:

ERROR: Extra data: line 1 column 4 (char 3)

This error started appearing suddenly and is now blocking our automated infrastructure provisioning and validation pipelines.
The failure occurs inside Azure CLI itself (JSON parsing stage) and exits with a non‑zero return code, causing downstream failures.
The issue is reproducible across multiple Azure CLI versions, so this does not appear to be version-specific.

Validated versions:

  "azure-cli": "2.84.0"
  
  "azure-cli": "2.85.0"

What Tried:

Tested with multiple Azure CLI versions (upgrade / downgrade).
Used --only-show-errors.
Separated stdout and stderr in scripts.
Implemented retry logic.
Verified the issue is not related to quota, SKU availability, or capacity constraints.

None of the above mitigations resolved the issue.

Observations:

The failure happens consistently when running commands similar to:

az vm create ... --vmss vmss

This indicates a CLI-side parsing failure, not a scripting or parameter issue.

Impact:

Blocks VM provisioning.
Breaks CI/CD validation pipelines.
Affects multiple Kubernetes distros (k3s, microk8s, RKE, etc.).
High operational impact.

Request/Help Needed:

We are looking for official guidance or a concrete fix for this scenario, specifically:

Is this a known Azure CLI issue related to:
- az vm create --vmss usage with VMSS Flexible orchestration?
1. Is there a recommended alternative (for example):
  - VMSS‑only provisioning
    - Explicit orchestration mode requirements
      - A CLI fix or workaround we should adopt
      1. Are there known backend/ARM response changes that could cause duplicate or malformed JSON responses?

Any confirmation, mitigation guidance, or fix recommendation would be extremely helpful, as this is currently blocking production validation workflows.

Jilakara Hemalatha 12,100 Reputation points Microsoft External Staff Moderator

2026-04-08T07:06:38.34+00:00
Hello Koteru,

Thank you for your patience while we continue investigating this issue. To better understand the behavior and help isolate the root cause, could you please assist us with the following details:

Could you share the exact Azure CLI command being used (with sensitive information masked), especially the usage of az vm create along with the --vmss parameter?

Could you clarify the intended outcome of this command (for example, whether you are trying to create a new VM within an existing VM Scale Set or associate a standalone VM to a VMSS)?

Please confirm the orchestration mode of the VM Scale Set (Flexible or Uniform).

Was the VM Scale Set created using Azure CLI, ARM templates, or another deployment method?

Could you provide details on the environment, including OS type, image used, and region where the deployment is being attempted?

Could you run the same command with the --debug flag and share the relevant portion of the output, particularly anything observed just before the error occurs?

When did this issue first start occurring, and were there any recent changes made to the CLI version, scripts, or VMSS configuration prior to the issue?

These details will help us determine whether the issue is related to command usage, orchestration mode, or a backend response behavior.
Koteru Reddy (LTIMindtree Limited) 85 Reputation points Microsoft External Staff

2026-04-08T07:24:19.0966667+00:00
Using below commands we are creating in the az cli task.

az vmss create -n vmss -g $RESOURCE_GROUP_KIND --platform-fault-domain-count 1

After created the vmss using above command running the below command to create the vm as part of vmss.

az vm create -n kind-master-node -g $RESOURCE_GROUP_KIND \ --image $OS_IMAGE --location $LOCATION --size $KIND_VM_SIZE --tags $tags \ --os-disk-size-gb $OS_DISK_SIZE_GB --vnet-name kind-vnet --vmss vmss \ --subnet kind-subnet --public-ip-sku Standard --admin-username kind \ --ssh-key-value kindkey.pub --nsg kind --assign-identity $AZ_WORKLOAD_IDENTITY_ID

Answer accepted by question author

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Your answer

Jilakara Hemalatha 12,100 Reputation points Microsoft External Staff Moderator

2026-04-08T07:06:38.34+00:00

Hello Koteru,

Thank you for your patience while we continue investigating this issue. To better understand the behavior and help isolate the root cause, could you please assist us with the following details:

Could you share the exact Azure CLI command being used (with sensitive information masked), especially the usage of az vm create along with the --vmss parameter?

Could you clarify the intended outcome of this command (for example, whether you are trying to create a new VM within an existing VM Scale Set or associate a standalone VM to a VMSS)?

Please confirm the orchestration mode of the VM Scale Set (Flexible or Uniform).

Was the VM Scale Set created using Azure CLI, ARM templates, or another deployment method?

Could you provide details on the environment, including OS type, image used, and region where the deployment is being attempted?

Could you run the same command with the --debug flag and share the relevant portion of the output, particularly anything observed just before the error occurs?

When did this issue first start occurring, and were there any recent changes made to the CLI version, scripts, or VMSS configuration prior to the issue?

These details will help us determine whether the issue is related to command usage, orchestration mode, or a backend response behavior.
Koteru Reddy (LTIMindtree Limited) 85 Reputation points Microsoft External Staff

2026-04-08T07:24:19.0966667+00:00

Using below commands we are creating in the az cli task.

az vmss create -n vmss -g $RESOURCE_GROUP_KIND --platform-fault-domain-count 1

After created the vmss using above command running the below command to create the vm as part of vmss.

az vm create -n kind-master-node -g $RESOURCE_GROUP_KIND \ --image $OS_IMAGE --location $LOCATION --size $KIND_VM_SIZE --tags $tags \ --os-disk-size-gb $OS_DISK_SIZE_GB --vnet-name kind-vnet --vmss vmss \ --subnet kind-subnet --public-ip-sku Standard --admin-username kind \ --ssh-key-value kindkey.pub --nsg kind --assign-identity $AZ_WORKLOAD_IDENTITY_ID

Answer 1

Thank you all for your support and guidance during the investigation.

The failure was confirmed to be unrelated to VMSS orchestration mode, capacity constraints, or backend (CRP) behavior. This was further validated with the Compute Resource Provider (CRP) team, who confirmed that no issues were observed from the service side and that the platform was functioning as expected.

Upon reviewing the debug logs, it was observed that the failure was occurring within Azure CLI during the image alias resolution phase. Specifically, a JSON parsing error (Extra data: line 1 column 4 (char 3)) was triggered before the VM provisioning request could be completed.

For this scenario, the issue was observed when using the image alias "Ubuntu2204", which may have led to inconsistent parsing of the alias metadata within Azure CLI. As a workaround, the image reference was updated to the fully qualified URN "Canonical:0001-com-ubuntu-server-jammy:22_04-lts:latest". Following this change, the command executed successfully, and VM provisioning completed without any errors.

Additionally, we would like to highlight that similar behaviors are being tracked in the Azure CLI GitHub repository:

We recommend monitoring the above threads for further updates or fixes from the Azure CLI team

Answer 2

Koteru Reddy (LTIMindtree Limited) 85 Microsoft External Staff

The issue got resolved after updated the vm size from Ubuntu2204 to

Canonical:0001-com-ubuntu-server-jammy:22_04-lts:latest

Let me do remaining distro validations and confirm you.

Mikael Dyrberg Lysdahl 0 Reputation points

2026-04-08T10:30:33.34+00:00

i am experiencing the same issue:

az vm create -n MyVm -g $env:AZURE_RESOURCE_GROUP --image Ubuntu2204

Extra data: line 1 column 4 (char 3)
Jilakara Hemalatha 12,100 Reputation points Microsoft External Staff Moderator

2026-04-08T11:59:14.11+00:00

Mikael Dyrberg Lysdahl

Can you run the command with --debug flag, it should show more info
Mikael Dyrberg Lysdahl 0 Reputation points

2026-04-08T14:16:07+00:00

az vm create -n MyVm -g $env:AZURE_RESOURCE_GROUP --image Ubuntu2204 --debug

cli.knack.cli: Command arguments: ['vm', 'create', '-n', 'MyVm', '-g', 'rg-dao-seaweedfs-test-dk', '--image', 'Ubuntu2204', '--debug']
Mikael Dyrberg Lysdahl 0 Reputation points

2026-04-08T14:20:05.3433333+00:00

can confirm i can create the vm with
Canonical:0001-com-ubuntu-server-jammy:22_04-lts:latest

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az vm create fails with "ERROR: Extra data: line 1 column 4 (char 3)" across multiple Azure CLI versions

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