Gateway - don't log updates on startup (#3421)

Only log "updating schema" if a previous schema exists

In the case of a new schema (on first load), log the service id,
variant, and mode on which the gateway is running.

packages/apollo-gateway/CHANGELOG.md

@@ -9,7 +9,7 @@
   1. Previously, the `experimental_didUpdateComposition` hook wouldn't be reliably called unless the `experimental_pollInterval` was set. If it _was_ called, it was sporadic and didn't necessarily mark the timing of an actual composition update. After this change, the hook is called on a successful composition update.
   2. The `experimental_pollInterval` configuration option now affects both the GCS polling interval when gateway is configured for managed federation, as well as the polling interval of services. The former being newly introduced behavior.
 * Gateway cached DataSource bug [#3412](https://github.com/apollographql/apollo-server/pull/3412) introduces a fix for managed federation users where `DataSource`s wouldn't update correctly if a service's url changed. This bug was introduced with heavier DataSource caching in [#3388](https://github.com/apollographql/apollo-server/pull/3388). By inspecting the `url` as well, `DataSource`s will now update correctly when a composition update occurs.
-
+* Gateway - don't log updates on startup [#3421](https://github.com/apollographql/apollo-server/pull/3421) Fine tune gateway startup logging - on load, instead of logging an "update", log the service id, variant, and mode in which gateway is running.
 # v.0.10.7
 
 > [See complete versioning details.](https://github.com/apollographql/apollo-server/commit/fc7462ec5f8604bd6cba99aa9a377a9b8e045566)

packages/apollo-gateway/src/index.ts

@@ -243,6 +243,12 @@ export class ApolloGateway implements GraphQLService {
 
   public async load(options?: { engine?: GraphQLServiceEngineConfig }) {
     await this.updateComposition(options);
+    const { graphId, graphVariant } = (options && options.engine) || {};
+    const mode = isManagedConfig(this.config) ? 'managed' : 'unmanaged';
+
+    this.logger.info(
+      `Gateway successfully loaded schema.\n\t* Mode: ${mode}${graphId ? `\n\t* Service: ${graphId}@${graphVariant || 'current'}`: ''}`,
+    );
     if (this.experimental_pollInterval) {
       setInterval(
         () => this.updateComposition(options),
@@ -292,15 +298,16 @@ export class ApolloGateway implements GraphQLService {
     ) {
       this.logger.debug('No change in service definitions since last check');
       return;
-    } else {
-      this.serviceDefinitions = result.serviceDefinitions;
+    }
+
+    if (previousSchema) {
+      this.logger.info('Gateway config has changed, updating schema');
     }
 
     this.compositionMetadata = result.compositionMetadata;
     this.serviceDefinitions = result.serviceDefinitions;
 
     if (this.queryPlanStore) this.queryPlanStore.flush();
-    this.logger.info('Gateway config has changed, updating schema');
 
     this.schema = this.createSchema(result.serviceDefinitions);
     try {