Merge pull request #9440 from hashicorp/f-append-logs

Append to debug log files, don't clobber.

helper/logging/logging.go

@@ -6,6 +6,7 @@ import (
 	"log"
 	"os"
 	"strings"
+	"syscall"
 
 	"github.com/hashicorp/logutils"
 )
@@ -31,7 +32,7 @@ func LogOutput() (logOutput io.Writer, err error) {
 	logOutput = os.Stderr
 	if logPath := os.Getenv(EnvLogFile); logPath != "" {
 		var err error
-		logOutput, err = os.Create(logPath)
+		logOutput, err = os.OpenFile(logPath, syscall.O_CREAT|syscall.O_RDWR|syscall.O_APPEND, 0666)
 		if err != nil {
 			return nil, err
 		}

website/source/docs/internals/debugging.html.md

@@ -12,7 +12,7 @@ Terraform has detailed logs which can be enabled by setting the `TF_LOG` environ
 
 You can set `TF_LOG` to one of the log levels `TRACE`, `DEBUG`, `INFO`, `WARN` or `ERROR` to change the verbosity of the logs. `TRACE` is the most verbose and it is the default if `TF_LOG` is set to something other than a log level name.
 
-To persist logged output you can set `TF_LOG_PATH` in order to force the log to always go 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.
+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.