What is a Remote Device; how does GTM monitor a remote data center?

Short answer

Remote Device is the definition made on the Remote Devices (Data Centers) screen so that a TR7 device running in another data center can be monitored from this device. GTM queries the WAN Access and LAN Access addresses in the definition at the Access Period interval (default 5 minutes); the remote device returns its CPU, memory, bandwidth, internet status, maintenance mode and the status and metrics of the vServices on it (the queried address must be defined in the Access Addresses list of the remote device). The result appears immediately as a status in the list and is passed to the five automatic health checks that are created on their own for each remote data center; these health checks change status with Required Success (default 2) and Required Failure (default 3) consecutive results and are used in health scenarios. The collected metrics are also used in health checks of the Datacenter HC type and in the data center sorting in Datacenter mode.

How Does It Work?

1. Query cycle: Each remote data center is queried separately at the Access Period interval (query mechanism).
2. WAN and LAN: First the addresses in the WAN list, then those in the LAN list are tried in order; in each list, the first address that responds is enough. The two lists are evaluated separately in every cycle; if one of them responds, the data center is considered reachable.
3. Information packet: The remote device returns CPU, Memory, BW, the internet status (the result of its own Internet Access Health Scenario), Maintenance Mode and the vService list.
4. Status and health checks: The status in the list shows the result of each query immediately (What do the Remote Device status values mean?). The automatic health checks, on the other hand, change according to the consecutive result thresholds:

Automatic health check	When it is OK
WAN access to <name> is successful	One of the WAN addresses responds.
LAN access to <name> is successful	One of the LAN addresses responds.
Access to <name> is successful	There is access over WAN or LAN.
<name> has internet access	The remote device reports that it has its own internet access.
<name> is under maintenance	The remote device is in maintenance mode.

Remote Devices in TR7

What	Where
Remote data center definition	Remote Devices (Data Centers) screen, Add: Name, WAN Access, LAN Access, Access Period, Required Success, Required Failure (add form).
This device's own definition	Settings in the bottom strip of the same screen: Local Datacenter Name, Access Addresses, Internet Access Health Scenario, Maintenance Mode (local data center settings).
Where it is used	The Disaster Recovery and Datacenter data center groups of domains, Health Scenarios conditions, Datacenter HC.
Monitoring	The Status, Last Check, Internet Status, WAN Access, LAN Access, CPU, Memory, BW columns in the list; the DC vServices row in the preview (preview).
Cluster	Each device queries the remote data center itself and keeps its own result.

Common Misconceptions

• "Adding a remote device changes DNS answers on its own." A remote device is an information source; the answer is affected only when its automatic health checks are used in a health scenario and bound to records, or when DC Based / Service Based sorting is selected in Datacenter mode.
• "Monitoring is two-way." The definition only makes this device monitor the other one; for monitoring in the other direction, the other device also adds this device to its own list.
• "The status in the list and the automatic health check change at the same time." The status is updated immediately at each query; the automatic health checks wait for as many consecutive results as Required Success / Required Failure.
• "Maintenance Mode pulls traffic away on its own." Maintenance Mode only makes the <name> is under maintenance health check OK; for the traffic to shift, this health check is used in a scenario (What are the Disaster Recovery conditions; is the switchover automatic or manual?).

How it is done in the documentation

• Remote Devices · What Is a Remote Device?
• Remote Devices · Its Place in the GTM Architecture
• Remote Devices · Operating Mechanism
• Health Checks · The Automatic Health Check Records

Related questions

• What do the Remote Device status values mean?
• How is traffic distributed across data centers in Datacenter mode?
• What is a health check in GTM; how does it differ from a Load Balancer health check?
• What are the basic building blocks of GTM?