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Sunday, 28 October 2012

Configuring CA signed certificates for ESXi 5.x hosts


This article guides you through the configuration of Certificate Authority (CA) certificates for a ESXi 5.x host. The instructions provided help you eliminate common causes for problems during certificate implementation, including configuration steps and details, and avoid misconfiguration in implementation of custom certificates in your environment.


Note: This article is part of several resolution paths. Before following the steps in this article, see Implementing CA signed SSL certificates with vSphere 5.0 (2015383) or Implementing CA signed SSL certificates with vSphere 5.1 (2034833).
Creating CA assigned certificates for an ESXi 5.x host is a complex task. In many organizations it is required to maintain proper security for regulatory requirements. Each server must be unique to the component as it ties to the fully qualified domain name of the server. As such you cannot just take a single certificate and apply it to all hosts. Wildcard certificates are currently not supported, but even if they were, it is much more secure to have a proper certificate for each host. There are several different work flows required for a successful implementation:
  • Creating the certificate request
  • Getting the certificate
  • Installation and configuration of the certificate on the ESXi host
These steps must be followed to ensure successful implementation of a custom certificate for an ESXi 5.x host. Before attempting these steps ensure that:
  • You have a vSphere 5.0 or vSphere 5.1 environment
  • You have followed the steps in the configuring SSL article
  • You have an SSH client (such as Putty) installed
  • You have a SFTP/SCP client (such as WinSCP) installed

Generating a certificate request

To generate a certificate request for an ESXi 5.x host:
  1. Launch a command prompt and navigate into the OpenSSL directory as previously configured in the Configuring OpenSSL article. By default this is C:\OpenSSL-Win32\bin.
  2. Execute the command:

    openssl req -new -nodes -out rui.csr -keyout rui.key -config openssl.cfg
    Note: There are no prompts because all information was provided in the openssl.cfg file as configured in the previous article.

    This will create the certificate request rui.csr.
When rui.csr is created, proceed to Getting the certificate.

Getting the certificate

After the certificate request is created, the certificate must be given to the certificate authority for generation of the actual certificate. The authority will present a certificate back, as well as a copy of their root certificate, if necessary. For the certificate chain to be trusted, the root certificate must be installed on the server.
Follow the appropriate section below for the steps for the certificate authority in question.
For Commercial CAs:
  1. Take the certificate request (rui.csr, as generated above) and send it to the authority in question.
  2. The authority will send back the generated certificate.
  3. Install the root certificate onto the vCenter server before proceeding to the Installation of the certificate section of this document.
For Microsoft CAs:
  1. Log in to the Microsoft CA certificate authority web interface. By default, it is http://<servername>/CertSrv/
  2. Click Request a certificate.
  3. Click advanced certificate request.
  4. Click Submit a certificate request by using a base-64-encoded CMC or PKCS #10 file, or submit a renewal request by using a base-64-encoded PKCS #7 file.
  5. Open the certificate request in a plain text editor.
  6. Copy from -----BEGIN CERTIFICATE REQUEST----- to -----END CERTIFICATE REQUEST----- into the Saved Request box.
  7. Click Web Server when selecting the Certificate Template.
  8. Click Submit to submit the request.
  9. Click Base 64 encoded on the Certificate issued screen.
  10. Click Download Certificate.
  11. Save the certificate on the desktop of the server as rui.crt. When complete, proceed to Installing and configuring the certificate on the ESXi host to complete the configuration of the custom certificate.
For OpenSSL Self-Signed Certificates:
  1. Create the certificate by running the command:

    openssl req -x509 -sha256 -newkey rsa:2048 -keyout rui.key -config openssl.cfg -out rui.crt -days 3650
    This command outputs the certificate as needed to proceed to the installation and configuration section of this article.

Installing and configuring the certificate on the ESXi host

After the certificate is created, complete the installation and configuration of the certificate on the ESXi 5.x host:
  1. Log in to vCenter Server
  2. Put the host into Maintenance Mode.
  3. Navigate to the console of the server to enable SSH on the ESXi 5.x host.
  4. Press F2 to log in to the Direct Console User Interface (DUCI).
  5. Click Troubleshooting options > Enable SSH.
  6. Log in to the host and then navigate to /etc/vmware/ssl.
  7. Copy the files to a backup location, such as a VMFS volume.
  8. Log in to the host with WinSCP and navigate to the /etc/vmware/ssl directory.
  9. Delete the existing rui.crt and rui.key from the directory.
  10. Copy the newly created rui.crt and rui.key to the directory using Text Mode or ASCII mode to avoid the issue of special characters ( ^M) appearing in the certificate file.
  11. Type less rui.crt to validate that there are no extra characters.

    Note: There should not be any erroneous ^M characters at the end of each line.
  12. Switch back to the DCUI of the host and select Troubleshooting Options > Restart Management Agents.
  13. When prompted press F11 to restart the agents. Wait until they are restarted.
  14. Press ESC several times until you logout of the DCUI.
  15. Exit the host from Maintenance Mode
When complete, the host is be made available and successfully rejoins the HA cluster. 
If you are not running vCenter Server 5.0 U1 or later, the configuration of VMware HA will fail with an error. This is due to a known issue where the new SSL thumbprint is not updated in the vCenter database for VMware HA. For more information on this error, see After upgrading to vSphere5, you see the HA error: vSphere HA Cannot be configured on this host because its SSL thumbprint has not been verified (2006210). The easiest way to resolve this issue is to follow the Alternative Workaroundsection of the KB article, which uses (attached to the article) to reconnect the servers to vCenter Server updating the expected SSL thumbprint in the vCenter Servr database. When complete, run a reconfigure of vSphere HA for the configuration to proceed successfully.
The configuration of the custom certificate is now complete. Repeat these steps for each host which needs to have a custom certificate.

Additional Information