microsoft/aspire · error · DistributedApplicationException

Failed to configure MongoDB replica set resource

Error message

Failed to configure MongoDB replica set resource '{resource.Name}' after {MaxRetriesAttempt} attempts.{(lastConfigurationError is null ? "" : $" The last error reported by MongoDB was: {lastConfigurationError.Message}")}

What it means

After exhausting MaxRetriesAttempt attempts to configure the MongoDB replica set (e.g. running `replSetInitiate`/`reconfig`), the library throws DistributedApplicationException stating configuration failed, optionally including the last error MongoDB itself reported. The replica set is at best partially configured at this point.

Solutions

Read the inner exception / 'last error reported by MongoDB' portion of the message for the actual server-side cause
Verify all member containers started and are reachable on their internal host:port before the replica set initializes
Check for configuration MongoDB permanently rejects (duplicate hosts, wrong member counts) - only the server's error distinguishes this from a transient race
Restart the app host; the library retries on the next run and often succeeds after transient races

Defensive patterns

Strategy: retry

Try / catch

try { /* run app host */ }
catch (DistributedApplicationException ex) when (ex.Message.Contains("Failed to configure MongoDB replica set")) { /* read inner exception for the server's last error; retry the run */ }

Prevention

Ensure members are healthy and reachable before initialization
Check the inner/last MongoDB error to distinguish transient races from permanent config rejections
Keep member host lists valid (no duplicates, correct count)

When it happens

Trigger: Every retry of replica set configuration hit a retryable error - MongoDB rejecting the configuration command, members unreachable, elections failing, or a configuration MongoDB will never accept (which fails identically to a transient race).

Common situations: Members not yet listening when config started; MongoDB rejecting member host lists (duplicate/unreachable hosts); network/DNS issues inside the container network; the server's last error message revealing the actual cause.

Understand the failure class

Background: Request timed out: what client-side request timeouts mean across libraries (Request timed out, TIMED_OUT, APITimeoutError) — this error's family across 39 libraries.

Related errors

AI-assisted analysis of microsoft/aspire@25830f84bd (2026-09-16). Data as JSON: /api/errors/4e8035d106f85456. Report an issue: GitHub.

Appendix: source

Thrown at src/Aspire.Hosting.MongoDB/ReplicaSet/MongoDBReplicaSetBuilderExtensions.cs:361

                                logger.LogInformation("MongoDB replica set member '{MemberName}' stopped accepting connections before initialization completed", initialPrimary.Resource.Name);
                            }
                        }

                        if (!configured && retries < MaxRetriesAttempt - 1)
                        {
                            logger.LogInformation("MongoDB replica set configuration retry attempt {Current}/{Max} will begin after {WaitIntervalSeconds} seconds", retries + 1, MaxRetriesAttempt, s_rsInitiationRetryWaitInterval.TotalSeconds);
                            await Task.Delay(s_rsInitiationRetryWaitInterval, ct).ConfigureAwait(false);
                        }
                    }

                    if (!configured)
                    {
                        // NOTE: Every attempt ran into a retryable error. The replica set is at best partially configured at
                        // this point, so it must not be reported as running.
                        // NOTE: The last error MongoDB gave is carried into the message, because a configuration it will
                        // never accept fails exactly like one that simply lost a race, and only the server's own
                        // explanation tells the two apart.
                        throw new DistributedApplicationException(
                            $"Failed to configure MongoDB replica set resource '{resource.Name}' after {MaxRetriesAttempt} attempts.{(lastConfigurationError is null ? "" : $" The last error reported by MongoDB was: {lastConfigurationError.Message}")}",
                            lastConfigurationError!);
                    }

                    rsResource.IsConfigured = true;
                    await evt.Notifications.PublishUpdateAsync(resource, s => s with
                    {
                        State = KnownResourceStates.Running,
                    }).ConfigureAwait(false);
                }
                catch (Exception ex)
                {
                    logger.LogCritical(ex, "Failed to initialize MongoDB replica set resource '{ResourceName}'", resource.Name);
                    await evt.Notifications.PublishUpdateAsync(resource, s => s with
                    {
                        State = KnownResourceStates.FailedToStart,
                    }).ConfigureAwait(false);
                }

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