Terraform has detailed logs that you can enable by setting the TF_LOG environment variable to any value. Enabling this setting causes detailed logs to appear on stderr.

You can set TF_LOG to one of the log levels (in order of decreasing verbosity) TRACE, DEBUG, INFO, WARN or ERROR to change the verbosity of the logs.

Setting TF_LOG to JSON outputs logs at the TRACE level or higher, and uses a parseable JSON encoding as the formatting.

Warning: The JSON encoding of log files is not considered a stable interface. It may change at any time, without warning. It is meant to support tooling that will be forthcoming, and that tooling is the only supported way to interact with JSON formatted logs.

Logging can be enabled separately for terraform itself and the provider plugins using the TF_LOG_CORE or TF_LOG_PROVIDER environment variables. These take the same level arguments as TF_LOG, but only activate a subset of the logs.

To persist logged output you can set TF_LOG_PATH in order to force the log to always be appended to a specific file when logging is enabled. Note that even when TF_LOG_PATH is set, TF_LOG must be set in order for any logging to be enabled.

If you find a bug with Terraform, please include the detailed log by using a service such as gist.