Troubleshooting Terraform

  1. Enabling Debug Log
  3. Dependency and Parallelism

Trace log with dependency analysis

Terraform is a great tool for managing infrastructure as code, but sometimes it can be tricky to debug when things go wrong. In this blog post, I’ll share tips on how to troubleshoot Terraform issues.

Enabling Debug Log

The TF_LOG environment variable allows you to set the log level for Terraform, which can be useful for getting more details about what Terraform is doing behind the scenes. You can set it to one of these values: TRACE, DEBUG, INFO, WARN, or ERROR. The default is INFO, which only shows high-level messages. To get more verbose output, you can set it to DEBUG. TRACE has details from DEBUG but has dependency analysis details that is not needed for most debugging. For example, you can run this command before running Terraform:

export TF_LOG=DEBUG and then terraform plan

or run it in single line

export TF_LOG=DEBUG && terraform plan

If you specify TF_LOG_PATH environment variable, log will store into the file.


The debug log can be massive and over 100MB! If you would like to focus on debugging provider you should use TF_LOG_PROVIDER with arguments from TF_LOG. If you suspect problem with dependency you should use TF_LOG_CORE.

Dependency and Parallelism

Terrafrom analyses dependencies between Terraform modules before execution. Dependency analysis ensure resources are provisioned in the correct order. Meanwhile, Terrafrom use the analysis result for efficient parallel execution of operations by identifying independent sets of resources that can be provisioned or modified concurrently. However, logs from concurrent execution is very difficult to read and we have to disable the concurrcy with parameter -parallelism=1 on plan and apply.

With -parallelism=1, whe resources are created/modified/destroyed one at a time, in sequence. This allows for easier debugging and troubleshooting, as each resource is executed one at a time. eg, terraform apply -parallelism=1:

Terraform Operation
Resource 1 Modification
Resource 2 Modification
Terraform Execution Completed

When -parallelism is not specify, default value is 10. The resources are created/modified/destroyed in parallel, allowing for faster execution. However, this can also make it more difficult to debug and troubleshoot issues, as multiple resources are executed simultaneously. eg, terraform apply:

Terraform Operation
Resource 1 Modification
Resource 2 Modification
Terraform Execution Completed