Article ID: 116240, created on Jun 6, 2013, last review on Aug 20, 2014

  • Applies to:
  • Operations Automation

Additional Information

This article describes the concept and purpose of load balancing rules for the QMail service used in POA.

When the QMail service is provisioned in a subscription, the system must decide which IP addresses and hostnames will be used for retrieving mail over POP, retrieving mail over IMAP, accepting mail from mail clients over SMTP, accepting mail from the Internet over SMTP.

For the single-host QMail service the IP addresses and hostname of the corresponding QMail host are already known because this host is managed by the system. The system uses this information to create and maintain the following DNS records:

Hostname Type Target Description
<the hostname of the QMail service host> A <the FrontNet IP address of the QMail service host> The DNS record is typically created by the provider.
pop.brand.com CNAME <the hostname of the QMail service host> The DNS record is automatically created by the system. It can be used for retrieving mail over POP (not recommended).
pop-ssl.brand.com CNAME <the hostname of the QMail service host> The DNS record is automatically created by the system. It is used for retrieving mail over POP (SSL). The pop-ssl.brand.com hostname is shown in CCP.
imap.brand.com CNAME <the hostname of the QMail service host> The DNS record is automatically created by the system. It can be used for retrieving mail over IMAP (not recommended).
imap-ssl.brand.com CNAME <the hostname of the QMail service host> The DNS record is automatically created by the system. It is used for retrieving mail over IMAP (SSL). The imap-ssl.brand.com hostname is shown in CCP.
outgoing-smtp.brand.com CNAME <the hostname of the QMail service host> The DNS record is automatically created by the system. It is used for accepting mail from mail clients over SMTP. The outgoing-smtp.brand.com hostname is shown in CCP.
smtp.brand.com A <the FrontNet IP address of the QMail service host> The DNS record is automatically created by the system. The smtp.brand.com hostname is used in MX DNS records of customer domains.
customer.com MX smtp.brand.com The DNS record is automatically created by the system. The DNS record is used for accepting mail from the Internet over SMTP.

Note: brand.com is the domain name of a brand. customer.com is the name of a customer domain.

For the clustered QMail service the system manages only nodes included into a QMail cluster. The provider manually configures a hardware or software load balancer for mail traffic. Then, the provider registers the corresponding load balancing rules in the system:

Address Port Protocol Algorithm Cluster Description
pop.loadbalancer.com 110 TCP Random <the name of the QMail cluster which the load balancing rule belongs to> The hostname from the Address field of the rule is used to construct DNS records for POP traffic. The system automatically finds the rule using the Port and Protocol fields.
pop-ssl.loadbalancer.com 993 TCP Random <the name of the QMail cluster which the load balancing rule belongs to> The hostname from the Address field of the rule is used to construct DNS records for POP (SSL) traffic. The system automatically finds the rule using the Port and Protocol fields.
imap.loadbalancer.com 143 TCP Random <the name of the QMail cluster which the load balancing rule belongs to> The hostname from the Address field of the rule is used to construct DNS records for IMAP traffic. The system automatically finds the rule using the Port and Protocol fields.
imap-ssl.loadbalancer.com 995 TCP Random <the name of the QMail cluster which the load balancing rule belongs to> The hostname from the Address field of the rule is used to construct DNS records for IMAP (SSL) traffic. The system automatically finds the rule using the Port and Protocol fields.
outgoing-smtp.loadbalancer.com 25 TCP Random <the name of the QMail cluster which the load balancing rule belongs to> The hostname from the Address field of the rule is used to construct DNS records for outgoing SMTP traffic. The system automatically finds the rule using the Port and Protocol fields.

Note: The 25/TCP port/protocol combination is not unique for SMTP traffic, so the system uses Custom Properties to select rules for incoming and outgoing SMTP traffic. Typically, the following Custom Property is added to the rule:

  • Name = ID
  • Value = Outgoing SMTP
<the load balancer’s FrontNet IP address for incoming SMTP traffic> 25 TCP Random <the name of the QMail cluster which the load balancing rule belongs to> The IP address from the Address field of the rule is used to construct DNS records for incoming SMTP traffic. The system automatically finds the rule using the Port and Protocol fields.

Note: The 25/TCP port/protocol combination is not unique for SMTP traffic, so the system uses Custom Properties to select rules for incoming and outgoing SMTP traffic. Typically, Custom Properties are not added to the rule.

When the clustered QMail service is provisioned in a subscription, the system looks for load balancing rules associated with the corresponding QMail cluster. Then, the system uses port/protocol combinations to obtain the corresponding load balancing rules.

For POP/IMAP traffic, port/protocol combinations are unique and the system automatically obtains the corresponding load balancing rules.

For incoming and outgoing SMTP traffic, the 25/TCP port/protocol combination is not unique, so the system must be supplied with additional information helping to automatically select the corresponding rules. To address this task, Custom Properties of load balancing rules and the SMTP load balancing rule ID string/Outgoing SMTP load balancing rule ID string Activation Parameters of Clustered QMail Resource Types are used. The system obtains the corresponding load balancing rule using the 25/TCP port/protocol combination and strings specified in the Activation Parameters and Custom Properties. Typically, the following configuration is used:

The first load balancing rule is created for outgoing SMTP traffic. The second load balancing rule is created is for incoming SMTP traffic.

The following Custom Property is added to the load balancing rule for outgoing SMTP traffic:

  • Name = ID
  • Value = Outgoing SMTP
No Custom Property is added to the load balancing rule for incoming SMTP traffic, because ambiguity is eliminated by the Custom Property of the load balancing rule for outgoing SMTP traffic.

In the Clustered QMail Resource Type the following Activation Parameters are specified:

  • Outgoing SMTP load balancing rule ID = Outgoing SMTP
  • SMTP load balancing rule ID string = EMPTY
Note: In general, several load balancing rules can be created for outgoing and incoming SMTP traffic. In this case these load balancing rules must be marked by different Custom Attributes and the corresponding strings must be specified in Clustered QMail Resource Types to eliminate ambiguity.

The obtained load balancing rules are used to create and maintain the following DNS records:

Hostname Type Target Description
pop.loadbalancer.com A <the load balancer’s FrontNet IP address for POP traffic> The DNS record is typically created by the provider.
pop-ssl-.loadbalancer.com A <the load balancer’s FrontNet IP address for POP (SSL) traffic> The DNS record is typically created by the provider.
imap.loadbalancer.com A <the load balancer’s FrontNet IP address for IMAP traffic> The DNS record is typically created by the provider.
imap-ssl.loadbalancer.com A <the load balancer’s FrontNet IP address for IMAP (SSL) traffic> The DNS record is typically created by the provider.
outgoing-smtp.loadbalancer.com A <the load balancer’s FrontNet IP address for outgoing SMTP traffic> The DNS record is typically created by the provider.
pop.brand.com CNAME pop.loadbalancer.com The DNS record is automatically created by the system. It can be used for retrieving mail over POP (not recommended).
pop-ssl.brand.com CNAME pop-ssl.loadbalancer.com The DNS record is automatically created by the system. It is used for retrieving mail over POP (SSL). The pop-ssl.brand.com hostname is shown in CCP.
imap.brand.com CNAME imap.loadbalancer.com The DNS record is automatically created by the system. It can be used for retrieving mail over IMAP (not recommended).
imap-ssl.brand.com CNAME imap-ssl.loadbalancer.com The DNS record is automatically created by the system. It is used for retrieving mail over IMAP (SSL). The imap-ssl.brand.com hostname is shown in CCP.
outgoing-smtp.brand.com CNAME outgoing-smtp.loadbalancer.com The DNS record is automatically created by the system. It is used for accepting mail from mail clients over SMTP. The outgoing-smtp.brand.com hostname is shown in CCP.
smtp.brand.com A <the load balancer’s FrontNet IP address for incoming SMTP traffic> The DNS record is automatically created by the system. The smtp.brand.com hostname is used in MX DNS records of customer domains.
customer.com MX smtp.brand.com The DNS record is automatically created by the system. The DNS record is used for accepting mail from the Internet over SMTP.

Note: brand.com is the domain name of a brand domain. customer.com is the name of a customer domain. loadbalancer.com is a DNS zone that is used for DNS records of the load balancer.

Important: All DNS records and load balancing rules are provided for illustration purposes. Actual DNS records and load balancing rules may differ from these examples.

See also: POA-63135

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