Write the Stackdriver config separately from the installation.

This will let us preinstall the Stackdriver logging agent but still
configure it correctly when bringing up new Windows nodes.

The hostname in the config file looks the same before-and-after:
  "logging.googleapis.com/local_resource_id" ${"k8s_node.e2e-test-peterhornyack-windows-node-group-6tw6"}
  "logging.googleapis.com/local_resource_id" ${"k8s_node.e2e-test-peterhornyack-windows-node-group-mf5r"}

cluster/gce/windows/configure.ps1

@@ -111,7 +111,10 @@ try {
   Set-EnvironmentVars
   Create-Directories
   Download-HelperScripts
-  InstallAndStart-LoggingAgent
+
+  Install-LoggingAgent
+  Configure-LoggingAgent
+  Restart-LoggingAgent
 
   Create-DockerRegistryKey
   Configure-Dockerd

cluster/gce/windows/k8s-node-setup.psm1

@@ -1091,12 +1091,13 @@ $STACKDRIVER_VERSION = 'v1-9'
 $STACKDRIVER_ROOT = 'C:\Program Files (x86)\Stackdriver'
 
 
-# Restart the Stackdriver logging agent
-# `Restart-Service StackdriverLogging` may fail because StackdriverLogging
-# sometimes is unstoppable, so we work around it by killing the processes.
-function Restart-StackdriverLoggingAgent {
+# Restarts the Stackdriver logging agent, or starts it if it is not currently
+# running. A standard `Restart-Service StackdriverLogging` may fail because
+# StackdriverLogging sometimes is unstoppable, so this function works around it
+# by killing the processes.
+function Restart-LoggingAgent {
   Stop-Service -NoWait -ErrorAction Ignore StackdriverLogging
- 
+
   # Wait (if necessary) for service to stop.
   $timeout = 10
   $stopped = (Get-service StackdriverLogging).Status -eq 'Stopped'
@@ -1132,13 +1133,13 @@ function Restart-StackdriverLoggingAgent {
   Start-Service StackdriverLogging
 }
 
-# Install and start the Stackdriver logging agent according to
+# Installs the Stackdriver logging agent according to
 # https://cloud.google.com/logging/docs/agent/installation.
 # TODO(yujuhong): Update to a newer Stackdriver agent once it is released to
 # support kubernetes metadata properly. The current version does not recognizes
 # the local resource key "logging.googleapis.com/local_resource_id", and fails
 # to label namespace, pod and container names on the logs.
-function InstallAndStart-LoggingAgent {
+function Install-LoggingAgent {
   # Remove the existing storage.json file if it exists. This is a workaround
   # for the bug where the logging agent cannot start up if the file is
   # corrupted.
@@ -1156,9 +1157,7 @@ function InstallAndStart-LoggingAgent {
     # well.
     Log-Output ("Skip: $STACKDRIVER_ROOT is already present, assuming that " +
                 "Stackdriver logging agent is already installed")
-    # Restart-Service restarts a running service or starts a not-running
-    # service.
-    Restart-StackdriverLoggingAgent
+    Restart-LoggingAgent
     return
   }
 
@@ -1174,25 +1173,35 @@ function InstallAndStart-LoggingAgent {
   Log-Output 'Invoking Stackdriver installer'
   Start-Process $installer_file -ArgumentList "/S" -Wait
 
+  # Install the record-reformer plugin.
   Start-Process "$STACKDRIVER_ROOT\LoggingAgent\Main\bin\fluent-gem" `
       -ArgumentList "install","fluent-plugin-record-reformer" `
       -Wait
 
-  # Create a configuration file for kubernetes containers.
-  # The config.d directory should have already been created automatically, but
-  # try creating again just in case.
-  New-Item "$STACKDRIVER_ROOT\LoggingAgent\config.d" `
-      -ItemType 'directory' `
-      -Force | Out-Null
-  $FLUENTD_CONFIG | Out-File `
-      -FilePath "$STACKDRIVER_ROOT\LoggingAgent\config.d\k8s_containers.conf" `
-      -Encoding ASCII
-
-  # Restart the service to pick up the new configurations.
-  Restart-StackdriverLoggingAgent
   Remove-Item -Force -Recurse $tmp_dir
 }
 
+# Writes the logging configuration file for Stackdriver. Restart-LoggingAgent
+# should then be called to pick up the new configuration.
+function Configure-LoggingAgent {
+  $fluentd_config_dir = "$STACKDRIVER_ROOT\LoggingAgent\config.d"
+  $fluentd_config_file = "$fluentd_config_dir\k8s_containers.conf"
+  if (-not (ShouldWrite-File $fluentd_config_file)) {
+    Log-Output ("Skip: fluentd logging config $fluentd_config_file already " +
+                "exists")
+    return
+  }
+
+  # Create a configuration file for kubernetes containers.
+  # The config.d directory should have already been created automatically, but
+  # try creating again just in case.
+  New-Item $fluentd_config_dir -ItemType 'directory' -Force | Out-Null
+  $config = $FLUENTD_CONFIG.replace('NODE_NAME', (hostname))
+  $config | Out-File -FilePath $fluentd_config_file -Encoding ASCII
+  Log-Output "Wrote fluentd logging config to $fluentd_config_file"
+}
+
+# The NODE_NAME placeholder must be replaced with the node's name (hostname).
 $FLUENTD_CONFIG = @'
 # This configuration file for Fluentd is used to watch changes to kubernetes
 # container logs in the directory /var/lib/docker/containers/ and submit the
@@ -1344,7 +1353,7 @@ $FLUENTD_CONFIG = @'
     "logging.googleapis.com/local_resource_id" ${"k8s_node.NODE_NAME"}
   </record>
 </filter>
-'@.replace('NODE_NAME', (hostname))
+'@
 
 
 # Export all public functions: