HTTP 502 status code (Bad Gateway)

An HTTP 502 status code (Bad Gateway) indicates that CloudFront wasn't able to serve the requested object because it couldn't connect to the origin server.

If you're using Lambda@Edge, the issue might be a Lambda validation error. If you receive an HTTP 502 error with the NonS3OriginDnsError error code, there's likely a DNS configuration problem that's preventing CloudFront from connecting to the origin.

SSL/TLS negotiation failure between CloudFront and a custom origin server

If you use a custom origin and you configured CloudFront to require HTTPS between CloudFront and your origin, the problem might be mismatched domain names. The SSL/TLS certificate that is installed on your origin includes a domain name in the Common Name field and possibly several more in the Subject Alternative Names field. (CloudFront supports wildcard characters in certificate domain names.) One of the domain names in the certificate must match one or both of the following values:

• The value that you specified for Origin Domain for the applicable origin in your distribution.

• The value of the Host header if you configured CloudFront to forward the Host header to your origin. For more information about forwarding the Host header to your origin, see Cache content based on request headers.

If the domain names don't match, the SSL/TLS handshake fails, and CloudFront returns an HTTP status code 502 (Bad Gateway) and sets the X-Cache header to Error from cloudfront.

To determine whether domain names in the certificate match the Origin Domain in the distribution or the Host header, you can use an online SSL checker or OpenSSL. If the domain names don't match, you have two options:

• The value that you specified for Origin Domain Name for the applicable origin in your distribution.

• The value of the Host header if you configured CloudFront to forward the Host header to your origin. For more information about forwarding the Host header to your origin, see Cache content based on request headers.

If the domain names don't match, the SSL/TLS handshake fails, and CloudFront returns an HTTP status code 502 (Bad Gateway) and sets the X-Cache header to Error from cloudfront.

To determine whether domain names in the certificate match the Origin Domain Name in the distribution or the Host header, you can use an online SSL checker or OpenSSL. If the domain names don't match, you have two options:

• Get a new SSL/TLS certificate that includes the applicable domain names.

  If you use AWS Certificate Manager (ACM), see Requesting a public certificate in the AWS Certificate Manager User Guide to request a new certificate.

• Change the distribution configuration so CloudFront no longer tries to use SSL to connect with your origin.

Online SSL checker

To find an SSL test tool, search the internet for "online ssl checker." Typically, you specify the name of your domain, and the tool returns a variety of information about your SSL/TLS certificate. Confirm that the certificate contains your domain name in the Common Name or Subject Alternative Names fields.

OpenSSL

To help troubleshoot HTTP 502 errors from CloudFront, you can use OpenSSL to try to make an SSL/TLS connection to your origin server. If OpenSSL is not able to make a connection, that can indicate a problem with your origin server's SSL/TLS configuration. If OpenSSL is able to make a connection, it returns information about the origin server's certificate, including the certificate's common name (Subject CN field) and subject alternative name (Subject Alternative Name field).

Use the following OpenSSL command to test the connection to your origin server (replace origin domain with your origin server's domain name, such as example.com):

openssl s_client -connect origin domain name:443

If the following are true:

• Your origin server supports multiple domain names with multiple SSL/TLS certificates

• Your distribution is configured to forward the Host header to the origin

Then add the -servername option to the OpenSSL command, as in the following example (replace CNAME with the CNAME that's configured in your distribution):

openssl s_client -connect origin domain name:443 -servername CNAME

Origin is not responding with supported ciphers/protocols

CloudFront connects to origin servers using ciphers and protocols. For a list of the ciphers and protocols that CloudFront supports, see Supported protocols and ciphers between CloudFront and the origin. If your origin does not respond with one of these ciphers or protocols in the SSL/TLS exchange, CloudFront fails to connect. You can validate that your origin supports the ciphers and protocols by using an online tool such as SSL Labs. Type the domain name of your origin in the Hostname field, and then choose Submit. Review the Common names and Alternative names fields from the test to see if they match your origin's domain name. After the test is finished, find the Protocols and Cipher Suites sections in the test results to see which ciphers or protocols are supported by your origin. Compare them with the list of Supported protocols and ciphers between CloudFront and the origin.

SSL/TLS certificate on the origin is expired, invalid, self-signed, or the certificate chain is in the wrong order

If the origin server returns the following, CloudFront drops the TCP connection, returns HTTP status code 502 (Bad Gateway), and sets the X-Cache header to Error from cloudfront:

• An expired certificate

• Invalid certificate

• Self-signed certificate

• Certificate chain in the wrong order

Note

If the full chain of certificates, including the intermediate certificate, is not present, CloudFront drops the TCP connection.

For information about installing an SSL/TLS certificate on your custom origin server, see Require HTTPS for communication between CloudFront and your custom origin.

Origin is not responding on specified ports in origin settings

When you create an origin on your CloudFront distribution, you can set the ports that CloudFront connects to the origin with for HTTP and HTTPS traffic. By default, these are TCP 80/443. You have the option to modify these ports. If your origin is rejecting traffic on these ports for any reason, or if your backend server isn't responding on the ports, CloudFront will fail to connect.

To troubleshoot these issues, check any firewalls running in your infrastructure and validate that they are not blocking the supported IP ranges. For more information, see AWS IP address ranges in the Amazon VPC User Guide. Additionally, verify whether your web server is running on the origin.

Lambda validation error

If you're using Lambda@Edge, an HTTP 502 status code can indicate that your Lambda function response was incorrectly formed or included invalid content. For more information about troubleshooting Lambda@Edge errors, see Test and debug Lambda@Edge functions.

DNS error (NonS3OriginDnsError)

An HTTP 502 error with the NonS3OriginDnsError error code indicates that there's a DNS configuration problem that prevents CloudFront from connecting to the origin. If you get this error from CloudFront, make sure that the origin's DNS configuration is correct and working.

When CloudFront receives a request for an object that's expired or is not in its cache, it makes a request to the origin to get the object. To make a successful request to the origin, CloudFront performs a DNS resolution on the origin domain. If the DNS service for your domain is experiencing issues, CloudFront can't resolve the domain name to get the IP address, which results in an HTTP 502 error (NonS3OriginDnsError). To fix this problem, contact your DNS provider, or, if you are using Amazon Route 53, see Why can't I access my website that uses Route 53 DNS services?

To further troubleshoot this issue, ensure that the authoritative name servers of your origin's root domain or zone apex (such as example.com) are functioning correctly. You can use the following commands to find the name servers for your apex origin, with a tool such as dig or nslookup:

dig OriginAPEXDomainName NS +short

nslookup -query=NS OriginAPEXDomainName

When you have the names of your name servers, use the following commands to query the domain name of your origin against them to make sure that each responds with an answer:

dig OriginDomainName @NameServer

nslookup OriginDomainName NameServer

Important

Make sure that you perform this DNS troubleshooting using a computer that's connected to the public internet. CloudFront resolves the origin domain using public DNS on the internet, so it's important to troubleshoot in a similar context.

If your origin is a subdomain whose DNS authority is delegated to a different name server than the root domain, make sure that the name server (NS) and start of authority (SOA) records are configured correctly for the subdomain. You can check for these records using commands similar to the preceding examples.

For more information about DNS, see Domain Name System (DNS) concepts in the Amazon Route 53 documentation.

Application Load Balancer origin 502 error

If you use Application Load Balancer as your origin and receive a 502 error, see How do I troubleshoot Application Load Balancer HTTP 502 errors?.

API Gateway origin 502 error

If you use API Gateway and receive a 502 error, see How do I resolve HTTP 502 errors from API Gateway REST APIs with Lambda proxy integration?.