No connection to firebase realtime database from cloud functions (in java)

Question

I have a function deployed in Google Cloud Functions (in Java) and while trying to access a Realtime database, there is no response at all - the only hint is that the moment I call:

query.addListenerForSingleValueEvent

I see a log entry:

Failed to find a usable hardware address from the network interfaces; using random bytes: f1:81:5a:ef:89:81:63:07

Here is my code (the function is triggered by receiving a message from the queue):

public class FetchGPWFunction implements BackgroundFunction<PubSubMessage> {
    private static final Logger logger = Logger.getLogger(FetchGPWFunction.class.getName());

    @Override
    public void accept(PubSubMessage message, Context context) {
        String data = message.data != null
                ? "Step 0.1 successful! with message: " + new String(Base64.getDecoder().decode(message.data))
                : "Step 0.1 successful!";
        logger.info(data);
        testFetchData();
    }

    private void testFetchData() {
        if (FirebaseApp.getApps().isEmpty()) {
            FirebaseApp.initializeApp();
            logger.info("Firebase application has been initialized");
        }
        DatabaseReference databaseReference = FirebaseDatabase.getInstance("https://projectid-rtdb.europe-west1.firebaseio.com").getReference();
        Query query = databaseReference.
                child("stockData").
                child("daily").
                child("pl").
                child("ALE").
                child("quotations").
                child("20201012").
                child("high");
        logger.info("launch query");
        final QueryResult queryResult = new QueryResult();
        query.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                logger.info("onDataChange >> got key=" + dataSnapshot.getKey() + " with value=" + dataSnapshot.getValue());
                queryResult.setDataSnapshot(dataSnapshot);
            }
            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                logger.severe("onCancelled >> ERROR! " + databaseError.getMessage() + " details=" + databaseError.getDetails());
                queryResult.setError(databaseError);
            }
        });

        int loopSafeGuard = 40;
        try {
            while (!queryResult.isDone() && (loopSafeGuard > 0)) {
                Thread.sleep(500);
                loopSafeGuard--;
            }
            logger.info("Loop ended with results: dataSnapshot=" + queryResult.getDataSnapshot() + " error=" + queryResult.getError());
        } catch (InterruptedException ie) {
            logger.info("Sleeping interrupted");
        }
    }

    public static class PubSubMessage {
        String data;
        Map<String, String> attributes;
        String messageId;
        String publishTime;
    }
}

(The query result is just a wrapper:

public class QueryResult {
    private DataSnapshot dataSnapshot = null;
    private DatabaseError error = null;
    
   ...
   
    public boolean isDone() {
        return ((dataSnapshot != null) || (error != null));
    }
}

And here are logs:

Info 2021-10-21 10:25:26.377 CEST functionFetchGPWData Firebase application has been initialized
Info 2021-10-21 10:25:26.420 CEST functionFetchGPWData launch query
Warning 2021-10-21 10:25:26.829 CEST functionFetchGPWData Failed to find a usable hardware address from the network interfaces; using random bytes: f1:81:5a:ef:89:81:63:07
Info 2021-10-21 10:25:46.463 CEST functionFetchGPWData Loop ended with results: dataSnapshot=null error=null
Debug 2021-10-21 10:25:46.467 CEST Function execution took 21311 ms, finished with status: 'ok'

No errors, no exceptions! - just this weird warning:

{
  "insertId": "000000-93ea514e-7271-4fe1-8b71-672b7d028ef7",
  "jsonPayload": {
    "message": "Failed to find a usable hardware address from the network interfaces; using random bytes: f1:81:5a:ef:89:81:63:07",
    "logging.googleapis.com/sourceLocation": {
      "method": "defaultMachineId",
      "file": "io/netty/util/internal/MacAddressUtil.java"
    }
  },
  "resource": {
    "type": "cloud_function",
    "labels": {
      "function_name": "functionFetchGPWData",
      "project_id": "projectid",
      "region": "europe-central2"
    }
  },
  "timestamp": "2021-10-21T08:25:26.829Z",
  "severity": "WARNING",
  "labels": {
    "execution_id": "waz43dlcibiy"
  },
  "logName": "projects/projectid/logs/cloudfunctions.googleapis.com%2Fcloud-functions",
  "trace": "projectid/traces/b812907333b0200b82f1323a1b5f7dcd",
  "sourceLocation": {
    "file": "io/netty/util/internal/MacAddressUtil.java"
  },
  "receiveTimestamp": "2021-10-21T08:25:35.103281657Z"
}

Is this a bug in cloud functions? Am I doing something wrong (more likely ;) ). I refuse to believe that a simple Realtime database read takes more then 20 seconds.

Answer 1

To wrap it up, this is another example of a Cloud Functions' cold start.

Although it's sometimes not possible to get rid of cold start completely, there are some GCP recommendations you can follow that might help reducing this effect.