In AWS Cloud watch, what is the difference between ELB_5xx and Http_5xx errors? And then there is also Backend_connection_errors.
HTTP errors served to the user can occur at either the load balancer or target level.
Any metrics that are prefixed with ELB originate at the load balancer level, there are many reasons why these can occur. For a 5XX error it could be a problem with connecting to your targets or could be that the throughput to the load balancer was too high (ELBs scale too based on traffic). More information about these errors are available in the Troubleshoot your Application Load Balancers document.
For the Http_ errors these will be coming from the target itself, essentially your application has returned this HTTP status back to the client. For debugging these you would look in your application logs to identify the root cause.
Related
My web application on AWS EC2 + load balancer sometimes shows 500 errors. How do I know if the error is on the server side or the application side?
I am using Route 53 domain and ssl on my url. I set the ALB redirect requests on port 80 to 443, and forward requests on port 443 to the target group (the EC2). However, the target group is returning 5xx error code sometimes when handling the request. Please see the screenshots for the metrics and configurations for the ALB.
Target Group Metrics
Target Group Configuration
Load Balancer Metrics
Load Balancer Listeners
EC2 Metrics
Right now the web application is running unsteady, sometimes it returns a 502 or 503 service unavailable (seems like it's a connnection timeout).
I have set up the ALB idle timeout 4000 secs.
ALB configuration
The application is using Nuxt.js + PHP7.0 + MySQL + Apache 2.4.54.
I have set the Apache prefork worker Maxclient number as 1000, which should be enough to handle the requests on the application.
The EC2 is a t2.Large resource, the CPU and Memory look enough to handle the processing.
It seems like if I directly request the IP address but not the domain, the amount of 5xx errors significantly reduced (but still exists).
I also have Wordpress application host on this EC2 in a subdomain (CNAME). I have never encountered any 5xx errors on this subdomain site, which makes me guess there might be some errors in my application code but not on the server side.
Is the 5xx error from my application or from the server?
I also tried to add another EC2 in the target group see if they can have at lease one healthy instance to handle the requests. However, the application is using a third-party API and has strict IP whitelist policy. I did some research that the Elastic IP I got from AWS cannot be attached to 2 different EC2s.
First of all, if your application is prone to stutters, increase healthcheck retries and timeouts, which will affect your initial question of flapping health.
To what I see from your screenshot, most of your 5xx are due to either server or application (you know obviously better what's the culprit since you have access to their logs).
To answer your question about 5xx errors coming from LB: this happens directly after LB kicks out unhealthy instance and if there's none to replace (which shouldn't be the case because you're supposed to have ASG if you enable evaluation of target health for LB), it can't produce meaningful output and thus crumbles with 5xx.
This should be enough information for you to make adjustments and logs investigation.
I've got an error 502 when I use google cloud balancer with CDN, the thing is, I am pretty sure I must have done something wrong setting up the load balancer because when I remove the load balancer, my website runs just fine.
This is how I configure my load balancer
here
Should I use HTTP or HTTPS healthcheck, because when I set up HTTPS
healthcheck, my website was up for a bit and then it down again
I have checked this link, they seem to have the same problem but it is not working for me.
I have followed a tutorial from openlitespeed forum to set Keep-Alive Timeout (secs) = 60s in server admin panel and configure instance to accepts long-lived connections ,still not working for me.
I have added these 2 firewall rules following this google cloud link to allow google health check ip but still didn’t work:
https://cloud.google.com/load-balancing/docs/health-checks#fw-netlb
https://cloud.google.com/load-balancing/docs/https/ext-http-lb-simple#firewall
When checking load balancer log message, it shows an error saying failed_to_pick_backend . I have tried to re-configure load balancer but it didn't help.
I just started to learn Google Cloud and my knowledge is really limited, it would be greatly appreciated if someone could show me step by step how to solve this issue. Thank you!
Posting an answer - based on OP's finding to improve user experience.
Solution to the error 502 - failed_to_pick_backend was changing Load Balancer from HTTP to TCP protocol and at the same type changing health check from HTTP to TCP also.
After that LB passes through all incoming connections as it should and the error dissapeared.
Here's some more info about various types of health checks and how to chose correct one.
The error message that you're facing it's "failed_to_pick_backend".
This error message means that HTTP responses code are generated when a GFE was not able to establish a connection to a backend instance or was not able to identify a viable backend instance to connect to
I noticed in the image that your health-check failed causing the aforementioned error messages, this Health Check failing behavior could be due to:
Web server software not running on backend instance
Web server software misconfigured on backend instance
Server resources exhausted and not accepting connections:
- CPU usage too high to respond
- Memory usage too high, process killed or can't malloc()
- Maximum amount of workers spawned and all are busy (think mpm_prefork in Apache)
- Maximum established TCP connections
Check if the running services were responding with a 200 (OK) to the Health Check probes and Verify your Backend Service timeout. The Backend Service timeout works together with the configured Health Check values to define the amount of time an instance has to respond before being considered unhealthy.
Additionally, You can see this troubleshooting guide to face some error messages (Including this).
Those experienced with Kubernetes from other platforms may be confused as to why their Ingresses are calling their backends "UNHEALTHY".
Health checks are not the same thing as Readiness Probes and Liveness Probes.
Health checks are an independent utility used by GCP's Load Balancers and perform the exact same function, but are defined elsewhere. Failures here will lead to 502 errors.
https://console.cloud.google.com/compute/healthChecks
I have configured a http external load balancer on GCP and all my vm instances are healthy in backend.
But when i am trying to access my server(installed on VM) from frontend static IP that is reserved at load balancer it is giving me 502 status error.
As a result of which i am unable to launch my application server using load balancer. Help me fix this issue.
Thanking you in advance.
To troubleshoot 502 response from the Load Balancer due to "failed_to_connect_to_backend." I would check the followings:
Usually, "failed_to_connect_to_backend" error message indicates that the load balancer is failing to connect to backends, investigating URL map rules is also a good point to start. I would also suggest reviewing your Load Balancer's URL map to make sure that Host rules, Path matcher, and Path rules are correctly defined and comply with descriptions in this article.
Also check if the backend instances are exhausting their resources, If a backend server is overwhelmed, it will refuse incoming requests, potentially causing the load balancer to give up on it and return the specific 502 error you're experiencing. Also, check the output on how many established connections are present at any one time using 'netstat' and watch command.
I would also recommend testing again with the HTTP(S) request directly to the instance, request the same URL that reporting 502. You might do this test in another VM instance in your VPC network.
maybe you should check if the time taken for the API to return the response is exceeded the timeout that will trigger the 502. The default value is 30 seconds.
Ref: https://cloud.google.com/load-balancing/docs/backend-service#timeout-setting
Looking for way to debug why backend for NIFI is failing. I created a NIFI cluster (verison 1.9.0, HDF 3.1.1.4, AMBARI 2.7.3) on Google cloud. Created HTTPS load balancer terminating https front end, and back end is the instance group for SSL enabled NIFI cluster. Getting a 502 back end error in the browser when I hit the url for the load balancer. Is there a way for Google Cloud to log the error ? There must be an error returned somewhere to troubleshoot the root cause. I don't see messages in the nifi log or the vm instance /var/log/messages. Stackdriver hasn't shown me errors. I created the keystore and truststore and followed the NIFI SSL enable instructions. It might be related to the SSL configs, or possibly firewall rules are not correct. But I am looking for some more helpful information to find the error.
If I am understanding the question properly, you are looking for a way to get HTTPS load balancer logs due to back end errors and your intention is to find out the root cause.Load balancer basically return 502 error due to unhealthy backend services or for unhealthy backend VM 's.If your stackdriver logging is enabled, you might get this log using advanced filter or can search by selecting the load balancer name and look for/search 502:
Advanced filter for 502 responses due to failures to connect to backends:
resource.type="http_load_balancer"
resource.labels.url_map_name="[URL Map]"
httpRequest.status=502
jsonPayload.statusDetails="failed_to_connect_to_backend"
Advanced filter for 502 responses due to backend timeouts:
resource.type="http_load_balancer"
resource.labels.url_map_name="[URL Map]"
httpRequest.status=502
jsonPayload.statusDetails="backend_timeout"
Advanced filter for 502 responses due to prematurely closed connections:
resource.type="http_load_balancer"
resource.labels.url_map_name="[URL Map]"
httpRequest.status=502
jsonPayload.statusDetails="backend_connection_closed_before_data_sent_to_client"
The URL Map is same as the name of the load balancer for HTTP(S) for cloud console.If we create the various components of the load balancer manually, need to use the URL Map for advanced filter.
Most common root causes for "failed_to_connect_to_backend" are: 1. Firewall blocking traffic, 2. Web server software not running on backend instance, 3. Web server software misconfigured on backend instance, 4. Server resources exhausted and not accepting connections (CPU usage too high to respond, Memory usage too high, process killed ,the maximum amount of workers spawned and all are busy, Maximum established TCP connections), 5. Poorly written server implementation struggling under load or non-standard behavior.
Most common root causes for “backend_timeout” are 1. the backend instance took longer than the Backend Service timeout to respond, meaning either the application is overloaded or the Backend Service Timeout is set too low, 2. The backend instance didn't respond at all (Crashing during a request).
Most Common Root causes for” backend_connection_closed_before_data_sent_to_client” is usually caused because the keepalive configuration parameter for the web server software running on the backend instance is less than the fixed (10 minute) keepalive (HTTP idle) timeout of the GFE. There are some situations where the backend may close a connection too soon while the GFE is still sending the HTTP request.
The previous response was spot on. The nifi ssl configuration is misconfigured, causing the backend health check to fail with a bad certificate. I will open a new question to address the nifi ssl configuration.
We are using cross region load balancing. When we get heavy traffic all at once, within 1 region, it begins to spin up new instances. While it is starting new instances, we get random HTTP 502 errors. Screenshots of configurations below. Is there any way to avoid the 502 errors while it is scaling up?
Image links of configuration below.
Instance Group Configuration (same setting on all regions)
Load Balancer
Thanks in advance for the help!
HTTP load balancer and the instances will have different external IPs.
1) Try accessing through one instance's external IP first to make sure the backend works. If it doesn't work, usually it's firewall settings problem.
2) HTTP 502 from load balancer usually indicates the health check of the load balancer thought the backend is unhealthy, check your health check config then.
See another similar question Google Load-balancer randomly failing requests to backend