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Troubleshoot App Engine errors
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This page describes the troubleshooting process for errors you might encounter while
using App Engine. For information about incidents affecting Google Cloud
services, refer to the Google Cloud Service Health Dashboard and All incidents reported for App Engine.
See the following pages for guidance on how to resolve issues related to your app:
App Engine troubleshooting strategies
The following sections explain how you can apply general troubleshooting
strategies to resolve your error. If you continue to encounter errors
even after following the steps in the troubleshooting guides, see What's next.
Output good logs using Cloud Logging
Troubleshooting your app running on App Engine is easier if you have good
application logs for debugging. Ensure your application writes logs in a way that
correlates request logs with the application logs.
With correlated logs you can identify the request that needs further analysis,
find the request trace, and analyze the root cause of the issue. For more
information on writing logs, see Write application logs.
Resolve unexpected latency
If you encounter issues with latency, do the following:
Check if the latency is affecting all requests to your service or only a
small percentage. The App Engine latency dashboard shows 50th,
95th, and 99th percentile latency.
If you have high latency on all three of these metrics, you have high latency
for at least 50% of your requests. If you only see high latency in the
99th percentile graph, you have high latency in 1% of your requests.
Identify the request with high latency to understand the source of
latency. You can use Cloud Trace or Cloud Logging to understand how
long a particular request has taken. For more information, see Understanding app latency.
To identify requests with high latency using Cloud Logging, apply the traceSampled=true filter to correlate logs in Cloud Logging with traces in Cloud Trace. For more information, see Integrate with Cloud Logging.
Try the following steps to fix latency issues, and improve service performance:
Consider using Profiler.
Modify your source code.
For more information on how to troubleshoot elevated latency issues, see Troubleshoot elevated latency in your app.
Resolve issues with connectivity
By default, your App Engine service is accessible on the public internet, however,
you can modify the service to have more restrictions on ingress and egress
network connectivity.
You can restrict ingress connections with the ingress settings, or through App Engine firewall rules. If you have trouble connecting to your App Engine service from
VPC networks or internet resources, check the following:
To resolve other connectivity issues, do the following:
For more information on how to troubleshoot connectivity issues, see
App Engine connectivity strategies.
What's next
If you can't find a solution to your problem in the App Engine
documentation, follow these steps:
For more information, see App Engine community.
Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.
Last updated 2025-08-29 UTC.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-29 UTC."],[[["\u003cp\u003eThis page provides troubleshooting guidance for errors encountered while using App Engine, along with links to relevant Google Cloud health and incident reports.\u003c/p\u003e\n"],["\u003cp\u003eTroubleshooting guides are available for common issues such as deployment, serving, and elevated latency.\u003c/p\u003e\n"],["\u003cp\u003eEffective logging, including correlating request and application logs, is crucial for debugging App Engine applications.\u003c/p\u003e\n"],["\u003cp\u003eLatency issues can be diagnosed by examining request metrics and utilizing tools like Cloud Trace and Cloud Logging, and fixed by adjusting instance classes, warmup requests, scaling settings, or code modification.\u003c/p\u003e\n"],["\u003cp\u003eConnectivity problems can be resolved by reviewing ingress settings, firewall rules, running network tests, and managing VPC connector configurations.\u003c/p\u003e\n"]]],[],null,["# Troubleshoot App Engine errors\n\nThis page describes the troubleshooting process for errors you might encounter while\nusing App Engine. For information about incidents affecting Google Cloud\nservices, refer to the [Google Cloud Service Health Dashboard](https://status.cloud.google.com/summary) and [All incidents reported for App Engine](https://status.cloud.google.com/products/kchyUtnkMHJWaAva8aYc/history).\n\nSee the following pages for guidance on how to resolve issues related to your app:\n\n- [Troubleshoot deployment issues](/appengine/docs/standard/troubleshooter/deployment)\n- [Troubleshoot serving issues](/appengine/docs/standard/troubleshooter/serving)\n- [Troubleshoot elevated latency in your app](/appengine/docs/standard/troubleshooter/latency)\n- [App Engine connectivity strategies](/appengine/docs/standard/troubleshooter/connectivity)\n\nApp Engine troubleshooting strategies\n-------------------------------------\n\nThe following sections explain how you can apply general troubleshooting\nstrategies to resolve your error. If you continue to encounter errors\neven after following the steps in the troubleshooting guides, see [What's next](#whats-next).\n\n### Output good logs using Cloud Logging\n\nTroubleshooting your app running on App Engine is easier if you have good\napplication logs for debugging. Ensure your application writes logs in a way that\n[correlates request logs with the application logs](/appengine/docs/standard/writing-application-logs#correlate_logs).\n\nWith correlated logs you can identify the request that needs further analysis,\nfind the request trace, and analyze the root cause of the issue. For more\ninformation on writing logs, see [Write application logs](/appengine/docs/standard/writing-application-logs#writing_app_logs).\n\n### Resolve unexpected latency\n\nIf you encounter issues with latency, do the following:\n\n1. Check if the latency is affecting all requests to your service or only a\n small percentage. The [App Engine latency dashboard](/appengine/docs/standard/monitoring-and-alerting-latency#checking_the_latency_dashboard) shows 50th,\n 95th, and 99th percentile latency.\n\n If you have high latency on all three of these metrics, you have high latency\n for at least 50% of your requests. If you only see high latency in the\n 99th percentile graph, you have high latency in 1% of your requests.\n2. Identify the request with high latency to understand the source of\n latency. You can use Cloud Trace or Cloud Logging to understand how\n long a particular request has taken. For more information, see [Understanding app latency](/appengine/docs/standard/monitoring-and-alerting-latency#understanding_app_latency).\n\n To identify requests with high latency using Cloud Logging, apply the `traceSampled=true` filter to correlate logs in Cloud Logging with traces in Cloud Trace. For more information, see [Integrate with Cloud Logging](/trace/docs/trace-log-integration).\n3. Try the following steps to fix latency issues, and improve service performance:\n\n - Increase the [instance class](/appengine/docs/standard#instance_classes) settings.\n\n - Reduce cold start latency by [configuring warmup requests](/appengine/docs/standard/configuring-warmup-requests).\n\n - Adjust [scaling settings](/appengine/docs/standard/how-instances-are-managed#scaling_dynamic_instances).\n\n \u003c!-- --\u003e\n\n - Consider using [Profiler](/appengine/docs/standard/cloud-profiler).\n\n - Modify your source code.\n\nFor more information on how to troubleshoot elevated latency issues, see [Troubleshoot elevated latency in your app](/appengine/docs/standard/troubleshooter/latency).\n\n### Resolve issues with connectivity\n\nBy default, your App Engine service is accessible on the public internet, however,\nyou can modify the service to have more restrictions on ingress and egress\nnetwork connectivity.\n\nYou can restrict ingress connections with the ingress settings, or through App Engine firewall rules. If you have trouble connecting to your App Engine service from\nVPC networks or internet resources, check the following:\n\n- [Ingress settings](/appengine/docs/standard/ingress-settings)\n- [App Engine firewall](/appengine/docs/standard/understanding-firewalls)\n\nTo resolve other connectivity issues, do the following:\n\n- Run a [network connectivity test](/network-intelligence-center/docs/connectivity-tests/how-to/running-connectivity-tests#console_6).\n\n- To resolve problems with traffic egress to a VPC network, check the VPC network\n firewall rules or use connection pooling in your client. For more information,\n see [Firewall rules](/vpc/docs/serverless-vpc-access#connector-fw-rules-standalone-vpc-or-host-prj).\n\n- Ensure that you aren't [overloading your VPC connector](/appengine/docs/standard/connecting-vpc#network-cpu) with more services and\n connections beyond its threshold. To improve throughput, consider the VPC connector\n size and instance count for your connectors. For more information, see\n [Serverless VPC Access](/vpc/docs/serverless-vpc-access#scaling).\n\n- For problems accessing VPC resources, review the [VPC connector throughput charts](/vpc/docs/serverless-vpc-access#throughput_chart).\n\nFor more information on how to troubleshoot connectivity issues, see\n[App Engine connectivity strategies](/appengine/docs/standard/troubleshooter/connectivity).\n\n### What's next\n\nIf you can't find a solution to your problem in the App Engine\ndocumentation, follow these steps:\n\n- Open a support case by contacting [Cloud Customer Care](/support-hub).\n- Get support from the community by [asking questions on StackOverflow](https://stackoverflow.com/questions/tagged/google-app-engine), or search for similar issues using the `google-app-engine` tag.\n- Open bugs or feature requests by using the [public issue tracker](/support/docs/issue-trackers).\n\nFor more information, see [App Engine community](/appengine/docs/standard/community)."]]
