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503 Service Unavailable - SSL Handshake Failure

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Symptom

The client application gets an HTTP status code of 503 Service Unavailable with the error code messaging.adaptors.http.flow.SslHandshakeFailed as a response for API calls.

Error message

Client application gets the following response code:

HTTP/1.1 503 Service Unavailable

In addition, you may observe the following error message:

{
   "fault":{
      "faultstring":"SSL Handshake failed sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target",
      "detail":{
         "errorcode":"messaging.adaptors.http.flow.SslHandshakeFailed"
      }
   }
}

Possible causes

You may get the status code 503 Service Unavailable with the error code messaging.adaptors.http.flow.SslHandshakeFailed due to a failure during the SSL handshake process between Apigee Edge’s Message Processor and the backend server for a number of reasons. The error message in the faultstring typically indicates a possible high level cause that has led to this error.

Depending on the error message observed in the faultstring, you need to use appropriate techniques to troubleshoot the issue. This playbook explains how to troubleshoot this error if you observe the error message SSL Handshake failed sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target in the faultstring.

This error occurs during the SSL handshake process between Apigee Edge’s Message Processor and the backend server:

  • If the truststore of Apigee Edge’s Message Processor:
    • Contains a certificate chain that does not match the backend server’s complete certificate chain, OR
    • Does not contain the backend server’s complete certificate chain
  • If the certificate chain presented by the backend server:
    • Contains Fully Qualified Domain Name (FQDN) that does not match the host name specified in the target endpoint
    • Contains an incorrect or incomplete certificate chain

The possible causes for this issue are as follows:

Cause Description Troubleshooting instructions applicable for
Incorrect/incomplete certificate or certificate chain in the Message Processor’s truststore The certificate and/or its chain stored in the truststore of Apigee Edge’s Message Processor does not match the backend server’s certificate chain or does not contain the backend server’s complete certificate chain. Edge Private and Public Cloud users
Mismatch of FQDN in the backend server’s certificate and the host name in target endpoint The certificate presented by the backend server contains a FQDN that does not match the host name specified in the target endpoint. Edge Private and Public Cloud users
Incorrect/incomplete certificate or certificate chain presented by backend server The certificate chain presented by the backend server is either incorrect or incomplete. Edge Private and Public Cloud users

Common diagnosis steps

Use one of the following tools/techniques to diagnose this error:

API Monitoring

Procedure #1: Using API Monitoring

To diagnose the error using API Monitoring:

  1. Sign in to Apigee Edge UI as a user with an appropriate role.
  2. Switch to the organization in which you want to investigate the issue.

  3. Navigate to the Analyze > API Monitoring > Investigate page.
  4. Select the specific timeframe in which you observed the errors.
  5. Plot Fault Code against Time.

  6. Select a cell which has the fault code messaging.adaptors.http.flow.SslHandshakeFailed as shown below:

    ( view larger image)

  7. Information about the fault code messaging.adaptors.http.flow.SslHandshakeFailed is displayed as shown below:

    ( view larger image)

  8. Click View logs and expand the row for the failed request.

    ( view larger image)

  9. From the Logs window, note the following details:
    • Request Message ID
    • Status Code: 503
    • Fault Source: target
    • Fault Code: messaging.adaptors.http.flow.SslHandshakeFailed

Trace

Procedure #2: Using Trace tool

To diagnose the error using the Trace tool:

  1. Enable the trace session and either
    • Wait for the 503 Service Unavailable error with error code messaging.adaptors.http.flow.SslHandshakeFailed to occur, or
    • If you can reproduce the issue, make the API call to reproduce the issue 503 Service Unavailable
  2. Ensure Show all FlowInfos is enabled:

  3. Select one of the failing requests and examine the trace.
  4. Navigate through different phases of the trace and locate where the failure occurred.
  5. You will find the error typically after the phase Target Request Flow Started as shown below:

    ( view larger image)

  6. Note the values of the following from the trace:
    • error: SSL Handshake failed sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    • error.cause: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
    • error.class: com.apigee.errors.http.server.ServiceUnavailableException
    • The value of the error SSL Handshake failed sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target indicates that the SSL Handshake failed, as Apigee Edge’s Message Processor was unable to validate the backend server’s certificate.
  7. Navigate to the AX (Analytics Data Recorded) Phase in the trace and click it.
  8. Scroll down to the Phase Details Error Headers section and determine the values of X-Apigee-fault-code and X-Apigee-fault-source, and X-Apigee-Message-ID as shown below:

    ( view larger image)

  9. Note the values of X-Apigee-fault-code, X-Apigee-fault-source, and X-Apigee-Message-ID:
  10. Error headers Value
    X-Apigee-fault-code messaging.adaptors.http.flow.SslHandshakeFailed
    X-Apigee-fault-source target
    X-Apigee-Message-ID MESSAGE_ID

Nginx

Procedure #3: Using Nginx access logs

To diagnose the error using Nginx access logs:

  1. If you are a Private Cloud user, then you can use Nginx access logs to determine the key information about HTTP 503 Service Unavailable.
  2. Check the Nginx access logs:

    /opt/apigee/var/log/edge-router/nginx/ORG~ENV.PORT#_access_log

  3. Search to see if there are any 503 errors with error code messaging.adaptors.http.flow.SslHandshakeFailed during a specific duration (if the problem happened in the past) or if there are any requests still failing with 503.
  4. If you do find any 503 errors with the X-Apigee-fault-code matching the value of messaging.adaptors.http.flow.SslHandshakeFailed, then determine the value of the X-Apigee-fault-source.

    Sample 503 error from Nginx access log:

    ( view larger image)

    The above sample entry from Nginx access log has the following values for X-Apigee-fault-code and X-Apigee-fault-source:

    Headers Value
    X-Apigee-fault-code messaging.adaptors.http.flow.SslHandshakeFailed
    X-Apigee-fault-source target

Message Processor logs

Procedure #4: Using Message Processor Logs

  1. Determine the message ID of one of the failing requests using API Monitoring, Trace tool, or Nginx Access Logs as explained in Common diagnosis steps.
  2. Search for the specific request message ID in the Message Processor log (/opt/apigee/var/log/edge-message-processor/logs/system.log). You may observe the following error:

    org:myorg env:test api:MyProxy rev:1
    messageid:myorg-28247-3541813-1
    NIOThread@1 ERROR HTTP.CLIENT - HTTPClient$Context.handshakeFailed() :
    SSLClientChannel[Connected: Remote:X.X.X.X:443
    Local:192.168.194.140:55102]@64596 useCount=1
    bytesRead=0 bytesWritten=0 age=233ms  lastIO=233ms
    isOpen=true handshake failed, message: General SSLEngine problem
    

    The above error indicates that the SSL handshake failed between the Message Processor and the backend server.

    This will be followed by an exception with detailed stack trace as shown below:

    org:myorg env:test api:MyProxy rev:1
    messageid:myorg-28247-3541813-1
    NIOThread@1 ERROR ADAPTORS.HTTP.FLOW - RequestWriteListener.onException() :
    RequestWriteListener.onException(HTTPRequest@1522922c)
    javax.net.ssl.SSLHandshakeException: General SSLEngine problem
    	at sun.security.ssl.Handshaker.checkThrown(Handshaker.java:1478)
    	at sun.security.ssl.SSLEngineImpl.checkTaskThrown(SSLEngineImpl.java:535)
    	... <snipped>
    Caused by: javax.net.ssl.SSLHandshakeException: General SSLEngine problem
    	at sun.security.ssl.Alerts.getSSLException(Alerts.java:203)
    	at sun.security.ssl.SSLEngineImpl.fatal(SSLEngineImpl.java:1728)
    	... <snipped>
    Caused by: sun.security.validator.ValidatorException: PKIX path building failed:
    sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid
    certification path to requested target
    	at sun.security.validator.PKIXValidator.doBuild(PKIXValidator.java:397)
    	at sun.security.validator.PKIXValidator.engineValidate(PKIXValidator.java:302)
    	... <snipped>
      

    Note the handshake failure is due to:

    Caused by: sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

    This indicates that the SSL Handshake failed as Apigee Edge’s Message Processor was unable to validate the backend server’s certificate.

Cause: Incorrect/incomplete certificate or certificate chain in the Message Processor’s truststore

Diagnosis

  1. Determine the Fault Code, Fault Source for the error observed using API Monitoring, Trace tool, or Nginx access logs as explained in Common diagnosis steps.
  2. If the Fault Code is messaging.adaptors.http.flow.SslHandshakeFailed, then determine the error message using one of the following methods:
  3. If the error message is sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target", then it indicates that the SSL Handshake failed, as Apigee Edge’s Message Processor was unable to validate the backend server’s certificate.

You can debug this issue in two phases:

  1. Phase 1: Determine the backend server’s certificate chain
  2. Phase 2: Compare the certificate chain stored in the Message Processor’s truststore

Phase 1

Phase 1: Determine the backend server’s certificate chain

Use one of the following methods to determine the backend server’s certificate chain:

openssl

Execute the openssl command against the backend server’s host name as follows:

openssl s_client -connect BACKEND_SERVER_HOST_NAME:PORT#

Note the Certificate chain from the output of the above command:

Sample backend server Certificate chain from the openssl command output:

Certificate chain
 0 s:/CN=mocktarget.apigee.net
   i:/C=US/O=Google Trust Services LLC/CN=GTS CA 1D4
 1 s:/C=US/O=Google Trust Services LLC/CN=GTS CA 1D4
   i:/C=US/O=Google Trust Services LLC/CN=GTS Root R1
 2 s:/C=US/O=Google Trust Services LLC/CN=GTS Root R1
   i:/C=US/O=Google Trust Services LLC/CN=GTS Root R1

tcpdump

  1. If you are a Public Cloud user, then capture the TCP/IP packets on the backend server.
  2. If you are a Private Cloud user, then you can capture the TCP/IP packets on the backend server or Message Processor. Preferably, capture them on the backend server as the packets are decrypted on the backend server.
  3. Use the following tcpdump command to capture TCP/IP packets:

    tcpdump -i any -s 0 host IP_ADDRESS -w FILE_NAME
    
  4. Analyze the TCP/IP packets using the Wireshark tool or similar tool with which you are familiar.

    Sample Analysis of Tcpdump

    ( view larger image)

    • Packet #43: The Message Processor (Source) sent a Client Hello message to the backend server (Destination).
    • Packet #44: The backend server acknowledges the receipt of the Client Hello message from the Message Processor.
    • Packet #45: The backend server sends the Server Hello message along with its certificate.
    • Packet #46: The Message Processor acknowledges the receipt of the Server Hello message and the certificate.
    • Packet #47: The Message Processor sends a FIN, ACK message followed by RST, ACK in Packet #48.

      This indicates that the backend server certificate validation by the Message Processor failed. It is because the Message Processor does not have any certificate that matches the backend server’s certificate or can’t trust the backend server’s certificate with the certificates available in its (Message Processor’s) truststore.

    • You can go back and review Packet #45 and determine the certificate chain sent by the backend server

      ( view larger image)

    • In this example, you can see that the server has sent a leaf certificate with the common name (CN) = mocktarget.apigee.net, followed by an intermediate certificate with CN= GTS CA 1D4 and root certificate with CN = GTX Root R1.

    If you’ve ascertained that the server’s certification validation failed, then go to Phase 2: Compare the backend server’s certificate and certificates stored in the Message Processor’s truststore.

Phase 2

Phase 2: Compare the backend server’s certificate and certificates stored in the Message Processor’s truststore

  1. Determine the backend server’s certificate chain.
  2. Determine the certificate stored in the Message Processor’s truststore using the following steps:
    1. Get the truststore reference name from the TrustStore element in the SSLInfo section in the TargetEndpoint.

      Let’s look at a sample SSLInfo section in a TargetEndpoint configuration:

      <TargetEndpoint name="default">
      ...
         <HTTPTargetConnection>
            <Properties />
            <SSLInfo>
               <Enabled>true</Enabled>
               <ClientAuthEnabled>true</ClientAuthEnabled>
               <KeyStore>ref://myKeystoreRef</KeyStore>
               <KeyAlias>myKey</KeyAlias>
               <TrustStore>
                  ref://myCompanyTrustStoreRef
               </TrustStore>
            </SSLInfo>
         </HTTPTargetConnection>
         ...
      </TargetEndpoint>
      
    2. In the above example, the TrustStore reference name is myCompanyTruststoreRef.
    3. In the Edge UI, select Environments > References. Note the name in the Reference column for the specific truststore reference. This will be your truststore name.

      ( view larger image)

    4. In the above example the truststore name is:

      myCompanyTruststoreRef: myCompanyTruststore

  3. Get the the certificates stored in the truststore (determined in the previous step) using the following APIs:

    1. Get all certificates for a keystore or truststore. This API lists all the certificates in the specific truststore.

      Public Cloud user:

      curl -v -X GET https//api.enterprise.apigee.com/v1/organizations/ORGANIZATION_NAME/environments/ENVIRONMENT_NAME/keystores/KEYSTORE_NAME/certs -H "Authorization: Bearer $TOKEN"
      

      Private Cloud user:

      curl -v -X GET http://MANAGEMENT_HOST:PORT_#/v1/organizations/ORGANIZATION_NAME/environments/ENVIRONMENT_NAME/keystores/KEYSTORE_NAME/certs -H "Authorization: Bearer $TOKEN"
      

      Where:

      • ORGANIZATION_NAME is the name of the organization
      • ENVIRONMENT_NAME is the name of the environment
      • KEYSTORE_NAME is the name of the keystore
      • $TOKEN is set to your OAuth 2.0 access token as described in Obtain an OAuth 2.0 access token
      • curl options used in this example are described in Use curl

      Sample output:

      The certificates from the example truststore myCompanyTruststore are:

      [
        "serverCert"
      ]
      
    2. Get Cert Details for the specific certificate from a Keystore or Truststore. This API returns the information about a specific certificate in the specific truststore.

      Public Cloud user:

      curl -v -X GET https//api.enterprise.apigee.com/v1/organizations/ORGANIZATION_NAME/environments/ENVIRONMENT_NAME/keystores/KEYSTORE_NAME/certs/CERT_NAME -H "Authorization: Bearer $TOKEN"
      

      Private Cloud user

      curl -v -X GET http://MANAGEMENT_HOST:PORT_#>/v1/organizations/ORGANIZATION_NAME/environments/ENVIRONMENT_NAME/keystores/KEYSTORE_NAME/certs/CERT_NAME -H "Authorization: Bearer $TOKEN"
      

      Where:

      • ORGANIZATION_NAME is the name of the organization
      • ENVIRONMENT_NAME is the name of the environment
      • KEYSTORE_NAME is the name of the keystore
      • CERT_NAME is the name of the certificate
      • $TOKEN is set to your OAuth 2.0 access token as described in Obtain an OAuth 2.0 access token
      • curl options used in this example are described in Use curl

      Sample Output

      Details of serverCert shows the subject and issuer as follows:

      Leaf/Entity Certificate:

      "subject": "CN=mocktarget.apigee.net",
      "issuer": "CN=GTS CA 1D4, O=Google Trust Services LLC, C=US",
      

      Intermediate Certificate:

      "subject" : "CN=GTS CA 1D4, O=Google Trust Services LLC, C=US",
      "issuer" : "CN=GTS Root R1, O=Google Trust Services LLC, C=US",
      
  4. Verify that the actual server certificate obtained in step 1 and the certificate stored in truststore obtained in step 3 match. If they do not match, then that’s the cause for the issue.

    From the example shown above, let’s look at one certificate at a time:

    1. Leaf certificate:

      From the backend server:

      s:/CN=mocktarget.apigee.net
      i:/C=US/O=Google Trust Services LLC/CN=GTS CA 1D4
      

      From Message Processor’s (client) truststore:

      "subject": "CN=mocktarget.apigee.net",
      "issuer": "CN=GTS CA 1D4, O=Google Trust Services LLC, C=US",
      

      The leaf certificate stored in the truststore matches that of the backend server.

    2. Intermediate certificate:

      From the backend server:

      s:/C=US/O=Google Trust Services LLC/CN=GTS CA 1D4
      i:/C=US/O=Google Trust Services LLC/CN=GTS Root R1
      

      From Message Processor’s (client) truststore:

      "subject" : "CN=GTS CA 1D4, O=Google Trust Services LLC, C=US",
      "issuer" : "CN=GTS Root R1, O=Google Trust Services LLC, C=US",
      

      The intermediate certificate stored in the truststore matches that of the backend server.

    3. Root certificate:

      From the backend server:

      s:/C=US/O=Google Trust Services LLC/CN=GTS Root R1
      i:/C=US/O=Google Trust Services LLC/CN=GTS Root R1
      

      The root certificate is completely missing in the Message Processor’s truststore.

    4. Since the root certificate is missing in the truststore, the Message Processor throws the following exception:

      sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
      

      and returns 503 Service Unavailable with the error code messaging.adaptors.http.flow.SslHandshakeFailed to the client applications.

Resolution

  1. Ensure that you have the proper and complete certificate chain of the backend server.
  2. If you are a Public Cloud user, follow the instructions in Update a TLS certificate for the Cloud to update the certificate to Apigee Edge’s Message Processor truststore.
  3. If you are a Private Cloud user, follow the instructions in Update a TLS certificate for the Private Cloud to update the certificate to Apigee Edge’s Message Processor truststore.

Cause: Mismatch of FQDN in the backend server’s certificate and the host name in target endpoint

If the backend server presents a certificate chain that contains FQDN, which does not match the host name specified in the target endpoint, then Apigee Edge’s Message Process returns the error SSL Handshake failed sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target.

Diagnosis

  1. Examine the specific target endpoint in the API proxy in which you are observing this error and note the backend server’s host name:

    Sample TargetEndpoint:

    <TargetEndpoint name="default">
       …
       <HTTPTargetConnection>
          <Properties />
          <SSLInfo>
             <Enabled>true</Enabled>
             <TrustStore>ref://myTrustStoreRef</TrustStore>
          </SSLInfo>
          <URL>https://backend.company.com/resource</URL>
       </HTTPTargetConnection>
    </TargetEndpoint>
    

    In the above example, the backend server’s host name is backend.company.com.

  2. Determine the FQDN in the backend server’s certificate using the openssl command as shown below:

    openssl s_client -connect BACKEND_SERVER_HOST_NAME>:PORT_#>
    

    For example:

    openssl s_client -connect backend.company.com:443
    

    Examine the section Certificate chain and note the FQDN specified as part of CN in the subject of the leaf certificate.

    Certificate chain
     0 s:/CN=backend.apigee.net
       i:/C=US/O=Google Trust Services LLC/CN=GTS CA 1D4
     1 s:/C=US/O=Google Trust Services LLC/CN=GTS CA 1D4
       i:/C=US/O=Google Trust Services LLC/CN=GTS Root R1
     2 s:/C=US/O=Google Trust Services LLC/CN=GTS Root R1
       i:/C=US/O=Google Trust Services LLC/CN=GTS Root R1
    

    In the above example, the backend server’s FQDN is backend.apigee.net.

  3. If the host name of the backend server obtained from step 1 and FQDN obtained step 2 do not match, then that’s the cause of the error.
  4. In the example discussed above, the host name in the target endpoint is backend.company.com. However, the FQDN name in the backend server’s certificate is backend.apigee.net. Since they do not match, you get this error.

Resolution

You can fix this issue by using one of the following methods:

Correct FQDN

Update backend server’s keystore with correct FQDN, valid and complete certificate chain:

  1. If you don’t have a backend server’s certificate with the correct FQDN, then procure the proper certificate from an appropriate CA (Certificate Authority).
  2. Validate that you have a valid and complete backend server’s certificate chain.

  3. Once you have the valid and complete certificate chain with the correct FQDN of the backend server in the leaf or entity certificate that is identical to the host name specified in the target endpoint, update the backend’s keystore with the complete certificate chain.

Correct backend server

Update the target endpoint with the correct backend server’s host name:

  1. If the host name was incorrectly specified in the target endpoint, then update the target endpoint to have the correct host name that matches the FQDN in the backend server’s certificate.
  2. Save the changes to the API proxy.

    In the example discussed above, if the backend server host name was incorrectly specified, then you can fix it by using the FQDN from the backend server’s certificate, that is backend.apigee.net as follows:

    <TargetEndpoint name="default">
       …
       <HTTPTargetConnection>
          <Properties />
          <SSLInfo>
             <Enabled>true</Enabled>
             <TrustStore>ref://myTrustStoreRef</TrustStore>
          </SSLInfo>
          <URL>https://backend.apigee.net/resource</URL>
       </HTTPTargetConnection>
    </TargetEndpoint>
    

Cause: Incorrect/incomplete certificate or certificate chain presented by backend server

Diagnosis

  1. Get the backend server’s certificate chain by executing the openssl command against the backend server’s host name as follows:
    openssl s_client -connect BACKEND_SERVER_HOST_NAME:PORT_#
    

    Note the Certificate chain from the output of the above command.

    Sample backend server Certificate Chain from the openssl command output:

    Certificate chain
     0 s:/CN=mocktarget.apigee.net
       i:/C=US/O=Google Trust Services LLC/CN=GTS CA 1D4
     1 s:/C=US/O=Google Trust Services LLC/CN=GTS CA 1D4
       i:/C=US/O=Google Trust Services LLC/CN=GTS Root R1
       
  2. Verify that you have the proper and complete certificate chain as explained in Validating certificate chain.
  3. If you don’t have the valid and complete certificate chain for the backend server, then that’s the cause for this issue.

    In the sample backend server’s certificate chain shown above, the root certificate is missing. Therefore, you get this error.

Resolution

Update backend server’s keystore with valid and complete certificate chain:

  1. Validate that you have a valid and complete backend server’s certificate chain.

  2. Update the valid and complete certificate chain in the backend server’s keystore.

If the problem still persists, go to Must gather diagnostic information.

Must gather diagnostic information

If the problem persists even after following the above instructions, gather the following diagnostic information and contact Apigee Support:

  • If you are a Public Cloud user, then provide the following information:
    • Organization name
    • Environment name
    • API Proxy name
    • Complete curl command to reproduce the error
    • Trace file showing the error
    • Output of the openssl command:

      openssl s_client -connect BACKEND_SERVER_HOST_NAME:PORT_#

    • TCP/IP packets captured on the backend server
  • If you are a Private Cloud user, provide the following information:
    • Complete error message observed
    • API proxy bundle
    • Trace file showing the error
    • Message Processor logs /opt/apigee/var/log/edge-message-processor/logs/system.log
    • Output of the openssl command:
      openssl s_client -connect BACKEND_SERVER_HOST_NAME:PORT_#
    • TCP/IP packets captured on the backend server or Message Processor.
    • Output of Get all certificates for a keystore or truststore API and also the details of each certificate obtained using Get Cert Details from a Keystore or Truststore API.

References