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Terraform
Plugin Development

Managing Log Output

Terraform binary, providers, and provider SDKs can all write logs that provide insight into operations and help you diagnose bugs. You can use environment variables to turn on logging, filter log output, choose the log format, and specify the log output path.

Enable Logging

Logging is off for all subsystems by default. To enable logging for a Terraform run, set one or more logging environment variables to either JSON format or a verbosity level. To write:

  • All logs for Terraform binary, providers, and provider SDKs, set TF_LOG. When you report bugs to issue trackers, we recommend setting TF_LOG=TRACE.
  • A subset of logs (e.g., for one provider), set the only the environment variables for your use case.

The following environment variables turn on logging and can help you filter log output. Some environment variables take precedence over others. For example, TF_LOG overrides all other logging variables. If you set TF_LOG=TRACE and TF_LOG_PROVIDER_AZUREM=WARN, all providers will write logs at the TRACE level.

VariableLogs Written ByPrecedence and Usage
TF_LOGAll loggers (Terraform, SDKs, providers)Overrides all other logging environment variables.
TF_LOG_CORETerraform binaryDoes not include providers.
TF_LOG_PROVIDERAll providers and provider SDKs used during the runOverrides logging environment variables for specific providers (e.g., TF_LOG_PROVIDER_AWS) and provider SDKs (e.g., TF_LOG_SDK). Only affects logs from Terraform CLI runs and does not affect logs from provider acceptance tests.
TF_LOG_PROVIDER_{PROVIDER_NAME} (e.g., TF_LOG_PROVIDER_AWS)Specific providerOnly applies to providers that write logs using the tflog package. Does not affect logs written by legacy log.Print* functions.
TF_LOG_SDKAll SDKs for providers used during the runOnly applies to logs written with terraform-plugin-log. For remaining SDKV2 logs, use TF_LOG or TF_LOG_PROVIDER.
TF_LOG_SDK_PROTOProtocol layer logging for providers built on terraform-plugin-go.Overrides TF_LOG_SDK.
TF_LOG_SDK_FRAMEWORKterraform-plugin-frameworkOverrides TF_LOG_SDK.
TF_LOG_SDK_HELPER_SCHEMAterraform-plugin-sdk/v2 helper/schema packageOverrides TF_LOG_SDK. Only applies to logs written with terraform-plugin-log. For remaining SDKV2 logs, use TF_LOG or TF_LOG_PROVIDER.
TF_LOG_SDK_MUXterraform-plugin-muxOverrides TF_LOG_SDK.

Log Levels

To specify logging verbosity, set a logging environment variable to one of the following values:

  • OFF - Turns off logging for that logger.
  • ERROR - Least verbose, typically provides more detail about user-facing errors.
  • WARN - Typically includes warnings about deprecations or other environment problems.
  • INFO - Can include details about run environment or configuration.
  • DEBUG - Can include additional details about behavior, especially behaviors that may be non-intuitive.
  • TRACE - Most verbose, typically includes low-level execution steps.

Important: Before Terraform v0.15.0, levels besides TRACE may not be reliable. This pull request has more details.

This example sets the loggers for all providers used in the run to WARN verbosity.

TF_LOG_PROVIDER=WARN

Log Format

By default, logs are written as plaintext lines, prefixed with a timestamp and the level in square braces.

YYYY-MM-DDTHH:MM:SS.SSSZ [Level] Message...

Explicitly setting the log format to JSON will output logs in a machine-readable format at the TRACE logging level. This format is not guaranteed to be stable between releases.

Output Path

Use TF_LOG_PATH to specify a file path where the log output file should be written. If you do not specify a log path, Terraform writes the specified log output to stderr.

Terraform can automatically create the output file at TF_LOG_PATH if it does not already exist. If the file does exist, Terraform adds new log output onto the end of the file without truncating the file contents.

Important: Do not write to stdout because our plugin system uses this as a communication channel.

Acceptance Testing

During testing, Terraform ignores TF_LOG_CORE, and logging environment variables only control the log output for the provider under test. The one exception is TF_LOG_PROVIDER. This is because TF_LOG_PROVIDER only affects logs that are produced through the Terraform CLI, and provider logs are not produced through the CLI during acceptance tests.

Refer to acceptance testing for additional environment variables that help you manage test log output.

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