This error occurs when Terraform provider plugins crash or lose communication with Terraform Core. Usually caused by provider bugs, invalid configurations, or incompatible versions. Upgrading providers and checking logs typically resolves the issue.
The "rpc error: code = Unavailable" error indicates that Terraform cannot communicate with a provider plugin through gRPC (the remote procedure call protocol used since Terraform v0.12). This happens when the provider process terminates unexpectedly, crashes with a panic, or closes its communication channel. The error message "transport is closing" often accompanies this, showing that the connection has been broken. This is typically not a Terraform Core issue but rather a provider-level problem that causes the plugin to exit or fail to respond.
Verify that your provider versions are compatible with your Terraform version. Upgrade to the latest provider versions as many RPC errors are fixed in newer releases.
terraform versionUpdate providers in your Terraform configuration:
terraform {
required_providers {
aws = {
source = "hashicorp/aws"
version = ">= 5.0" # Use latest stable version
}
}
}Then run:
terraform init -upgradeTerraform debug logs often reveal the underlying panic or error in the provider. Set the TF_LOG environment variable before running your command:
export TF_LOG=DEBUG
terraform plan > terraform_debug.log 2>&1After running the command, examine the log file for panic stack traces or specific error messages that indicate what the provider is failing on. Look for lines containing "panic:" to find the exact issue.
grep -i "panic:" terraform_debug.logInvalid or null values in your configuration can trigger provider crashes. Ensure all required resource attributes have valid values. Check for:
- Variables that might be null or undefined
- Missing required provider arguments
- Invalid data types or malformed values
terraform validateReview your variables file and confirm all required values are set:
# Ensure required variables are defined and not null
variable "vpc_id" {
type = string
validation {
condition = can(regex("^vpc-", var.vpc_id))
error_message = "VPC ID must be a valid AWS VPC ID."
}
}If multiple resources are causing issues, use the -target flag to run Terraform against specific resources. This helps identify which resource is triggering the provider crash:
terraform plan -target='aws_instance.example'
terraform apply -target='aws_instance.example'Once you identify the problematic resource, examine its configuration carefully for invalid values or unsupported combinations.
Sometimes a corrupted state file can cause provider communication issues. Back up your state and reinitialize:
# Backup current state
cp terraform.tfstate terraform.tfstate.backup
# Remove lock file if it exists
rm .terraform.lock.hcl
# Reinitialize
terraform initVerify the state is valid:
terraform state list
terraform state show <resource>If after upgrading providers and validating your configuration the error persists, it likely indicates a provider bug. Collect diagnostic information and report it to the provider's GitHub repository:
1. Save the debug log output from step 2
2. Note your Terraform and provider versions
3. Provide a minimal configuration that reproduces the issue
4. Open an issue on the provider's GitHub repository (e.g., https://github.com/hashicorp/terraform-provider-aws/issues)
Include the panic message from your debug logs, as this helps maintainers identify and fix the underlying bug.
gRPC and Plugin Protocol: Terraform v0.12+ uses gRPC for provider communication. The "Unavailable" error code specifically means the RPC connection cannot be established or was closed unexpectedly. This is different from timeouts or context cancellations.
Provider Panics: Many RPC errors are caused by provider panics. Common panic types include interface conversion errors (e.g., "interface {} is []interface {}, not string") and nil pointer dereferences. These are provider bugs, not Terraform issues.
State Consistency: Even if a provider crashes, resources may already be created in the cloud provider. After fixing the underlying issue, you may need to import existing resources back into your state file to maintain consistency.
Resource Limits: In some cases, having too many concurrent provider instances (e.g., 8+ parallel Azure subscriptions) can overwhelm the plugin process. Consider reducing parallelism with terraform apply -parallelism=2.
Rate Limiting: Some providers implement internal rate limiting. If you're performing large-scale operations, the provider may timeout or crash. Add explicit delays or reduce the number of concurrent operations.
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