Extend Remote Config with Cloud Functions

You can trigger a function in response to Remote Config events, including the publication of a new config version or the rollback to an older version. This guide describes how to create a Remote Config background function that performs a diff of two template versions.

Trigger a Remote Config function

To define a handler for Remote Config events, use the functions.remoteConfig module's onUpdate() function. The TemplateVersion object returned by onUpdate contains the key metadata fields for a template update such as the version number and time of the update. You can also retrieve the email for the user who made the update, with name and an image if available.

Here's an example of a Remote Config function that returns a diff of each updated version and the version it replaced. The function examines the versionNumber field of the template object and retrieves the current (newly updated) version together with the version one number lower:

exports.showConfigDiff = functions.remoteConfig.onUpdate(versionMetadata => {
  return admin.credential.applicationDefault().getAccessToken()
    .then(accessTokenObj => {
      return accessTokenObj.access_token;
    .then(accessToken => {
      const currentVersion = versionMetadata.versionNumber;
      const templatePromises = [];
      templatePromises.push(getTemplate(currentVersion, accessToken));
      templatePromises.push(getTemplate(currentVersion - 1, accessToken));

      return Promise.all(templatePromises);
    .then(results => {
      const currentTemplate = results[0];
      const previousTemplate = results[1];

      const diff = jsonDiff.diffString(previousTemplate, currentTemplate);


      return null;
    }).catch(error => {
      return null;

This sample uses the json-diff and request-promise modules to create the diff and build the request to get the template object. For a sample that incorporates Remote Config client logic as well as Firebase Cloud Messaging, see Propagate Remote Config updates in real time.