When should I use a Backend Group, and when individual Backend Services?

Short answer

A Backend Group is used for more than one server that offers the same service and will work with the same settings: in the group, all settings other than the address, Weight, Connection Limit and Cookie Content (health check, SSL, SNAT, Proxy, Maintenance Mode, Backup Service) are applied in common to all servers of the group. If there is a single server, if the servers require different settings, or if a single server needs to be put into maintenance or only some servers need to be made backups, individual Backend Services are used.

How Does It Work?

• Backend Group: The settings are entered once, at group level. The servers are added as rows to the Backends table; in a row, only the address (IP or domain name, and port), Weight, Connection Limit and Cookie Content are specific to the server. TR7 runs each row as a separate server with the common settings of the group.
• In a group, the health check is also per server: The profile is selected at group level, but each server is checked separately; a server that goes down is taken out of traffic on its own. The Health indicator of the group shows that status if the statuses of the members are the same, and Partially healthy if they differ.
• Individual Backend Service: Each server is a separate record, and each of its settings is made separately.
• Both are selected in the same place in the Default Backend Services list and the Conditional Backend Services (Content Switching) sets of the vService; groups and individual Backend Services can be used together in one vService.

Decision Table

Need	Recommended	Why
The servers use the same health check, SSL, SNAT and Proxy settings	Backend Group	The settings are managed from a single place
Servers are added or removed frequently	Backend Group	A new row takes the settings of the group automatically; no change is needed on the vService
The servers need to be put into maintenance one by one	Individual Backend Services	In a group, Maintenance Mode puts all servers into maintenance together
Only some of the servers will be backups	An individual Backend Service or a separate backup group	In a group, Backup Service is applied to all servers
The servers require different SSL or health check settings	Individual Backend Services or separate groups	These settings are common in a group
The weight, connection limit or Cookie Content value of the servers differs	Backend Group	These four fields are entered per server in a group as well
There is a single server and it will remain single	Individual Backend Service	The advantage of a group appears with more than one server; if the number of servers will increase, a group can also be used (Should I create a Backend Group even if I only have one server?)

In TR7

• Backend Group: Load Balancer → Backend Groups → Add; the servers are entered as rows in the Backends table.
• Individual Backend Service: Load Balancer → Backend Services → Add.
• Which setting is common: Which settings are shared at group level, and which are per server?
• The decision guide in docs: Backend Groups · When should a Backend Group be used?

Common Misconceptions

• "I can put a single server in a group into maintenance." Maintenance Mode is at group level; all servers go into maintenance together. To put a single server into maintenance, the server is defined as an individual Backend Service or its row is removed from the group.
• "In a group, I give different health checks to different servers." The profile is at group level; each server is checked separately, but the profile is the same.
• "If one server in a group goes down, the whole group is taken out of traffic." The check is per server; only the server that goes down is taken out of traffic, and the group indicator becomes Partially healthy.
• "A group and an individual Backend Service cannot be used together in one vService." Both can be added to the same list.

How it is done in the documentation

• Backend Groups · Backend Group and Backend Service Comparison
• Backend Groups · When should a Backend Group be used?
• Backend Groups · When should an individual Backend Service be used?
• Backend Groups · Backends

Related questions

• What is a Backend Group, and how is it different from a Backend Service?
• Should I create a Backend Group even if I only have one server?
• Which settings are shared at group level, and which are per server?