Description

Removing theresource_monitoring block from acoder_agent resource causes a panic with "index out of range [0] with length 0" error when starting workspaces. This appears to be a long-standing issue that affects workspace functionality when users attempt to disable resource monitoring.

Note: The issue occurs both when completely removing the block AND when replacing the content with empty braces{}.

Expected Behavior

• Removing theresource_monitoring block should either:
  1. Allow the workspace to start normally without monitoring (if this is intended to be optional)
  2. Provide a clear validation error explaining thatresource_monitoring is required
• Emptyresource_monitoring {} blocks should either be handled gracefully or validated properly

Actual Behavior

• Workspace fails to start with a panic
• Error message:The plugin.(*GRPCProvider).PlanResourceChange request was cancelled.
• Stack trace shows:panic: runtime error: index out of range [0] with length 0

Steps to Reproduce

1. Create a template with acoder_agent resource that includes aresource_monitoring block
2. Successfully deploy workspaces using this template
3. Either:
   • Remove the entireresource_monitoring block from thecoder_agent resource, OR
   • Replace theresource_monitoring content with empty braces:resource_monitoring {}
4. Update the template
5. Attempt to start a workspace

Environment

• Provider Version: v2.10.0 (also reproduced in v2.8.0 and v2.4.0)
• Test platform: Coder 2.25.1

Example Configuration

Working configuration:

resource"coder_agent""main" {os="linux"arch="amd64"resources_monitoring {memory {enabled=truethreshold=90    }volume {path="/home/coder"enabled=truethreshold=80    }  }}

Failing configurations:

Option 1 - Completely removed:

resource"coder_agent""main" {os="linux"arch="amd64"# resource_monitoring block removed entirely}

Option 2 - Empty block:

resource"coder_agent""main" {os="linux"arch="amd64"resources_monitoring {# empty block - also causes panic  }}

Additional Context

• This issue has been consistent across multiple provider versions (v2.4.0, v2.8.0, v2.10.0)
• The panic occurs at runtime when starting workspaces, not during template validation
• Template can be uploaded successfully, but workspace creation fails
• Rolling back the provider version does not resolve the issue once theresource_monitoring block is removed or emptied
• The error specifically affects line 86 in the customer's template (thecoder_agent resource)
• Both complete removal and empty block replacement ({}) are equally destructive

Customer Impact

• Prevents users from disabling resource monitoring when desired
• Causes workspace startup failures
• Requires keeping resource monitoring enabled with actual content even when not needed
• No graceful way to disable monitoring functionality

Suggested Solutions

1. If resource_monitoring is optional: Fix the panic by properly handling the case where the block is absent or empty
2. If resource_monitoring is required: Add proper validation to prevent template upload/update when the block is missing or empty
3. Feature enhancement: Allow explicit disabling of resource monitoring with a boolean flag or handle empty blocks gracefully
4. Validation improvement: Provide clear error messages during template validation rather than runtime panics

Classification

This issue sits between a bug report and feature request:

• Bug aspect: The panic and poor error handling when the block is removed or emptied
• Feature aspect: The ability to optionally disable resource monitoring