Automatic MID Server selection

  • Release version: Yokohama
  • Updated January 30, 2025
  • 2 minutes to read
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    Summary of Automatic MID Server selection

    Automatic MID Server selection enables ServiceNow agents to connect to the most efficient MID Server available by performing connectivity tests based on latency and current load. This feature, part of the Agent Client Collector (ACC), is disabled by default and serves primarily as a fail-over mechanism rather than a full load balancer. It helps keep the back-end URL list on the agent host updated without additional workflows.

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    Key Features

    • Dynamic MID Server Selection: Agents receive a list of MID Servers and select a primary and secondary MID Server to optimize connection efficiency and provide fail-over protection.
    • Capability-Based Filtering: MID Servers configured with Agent Client Collector capabilities are eligible for selection, allowing agents to connect only to suitable MID Servers.
    • Automatic Configuration Updates: Periodic updates from the ServiceNow instance maintain an up-to-date list of available MID Servers on agents.
    • Unified Key Store Security: Communication between agents and MID Servers is secured using the MID Server’s unified key store.

    Considerations for Use

    • Automatic selection is not a true load balancer; it is best used for fail-over scenarios.
    • Configuration complexity increases due to multiple input sources determining back-end URLs, unlike single URL setups with dedicated load balancers.
    • Agents may attempt to connect to MID Servers in restricted areas, potentially triggering security alerts.
    • Network environments with frequently changing DNS contexts, such as end-user systems switching between corporate, Wi-Fi, VPN, or external networks, may experience reconnection issues.
    • DNS resolution is performed periodically and can affect connection behavior.

    How to Enable and Configure

    • Enable automatic MID Server selection in your ServiceNow instance to allow agents to test connections and select the most efficient MID Server.
    • Configure MID Servers with the appropriate Agent Client Collector capabilities to define eligibility for automatic selection.
    • Explicitly configure and exclude MID Servers that should not connect to certain agents, for example due to firewall or security restrictions.
    • Use the MID Server unified key store to secure agent-to-MID Server communication.

    Expected Outcomes

    By enabling automatic MID Server selection, ServiceNow customers can expect more efficient and resilient connections between agents and MID Servers, reducing manual configuration overhead for back-end URLs and improving fail-over handling. However, customers should carefully evaluate their network environment, DNS setup, and security policies to ensure compatibility and avoid connectivity or security issues.

    Automatic selection of MID Servers ensures that each agent uses the most efficient available MID Server.

    The Agent Client Collector automatic MID Server selection feature set is disabled by default. There are several factors to consider before determining if automatic MID Server selection is right for your use cases.

    Use case considerations

    Automatic MID Server selection provides several benefits. MID Server capabilities can narrow the list of MID Servers an agent can potential connect to. Automatic MID Server selection keeps the back-end URL configuration list up to date on the agent host without additional work flows.

    When automatic MID Server selection is enabled, the agent performs a connectivity test against the list of available MID Servers and determines the best connection based on latency and number of currently connected agents.

    However, there are several additional considerations that may make automatic MID Server selection wrong for your use case.

    The ACC automatic MID Server selection is not a true load balancer and should be considered a fail-over mechanism. There is higher complexity for choosing a back-end URL as it is derived from multiple input sources. If, instead, an application load balancer is used only one back-end URL needs to be specified. See Enable the Agent Client Collector load balancer for more information.

    By default, each agent is sent the list of all MID Servers listening for ACC connections. Since that list includes MID Servers running in restricted areas, the agents can try to connect to them which can generate security alerts.

    Your DNS configuration should be considered before using automatic MID Server selection because the resolution can lead to unexpected results. The DNS resolution is done periodically. End User Compute systems that alternate between internal corporate, Wi-Fi, VPN, or external networks may not be able to reconnect if the network context has changed.

    Automatic selection process

    When automatic selection is enabled, the ServiceNow instance sends periodic MID Server updates to existing agents. The agent selects a MID Server based on information it receives from the ServiceNow instance.

    During automatic MID Server selection, the agent selects a primary MID and a secondary MID list, and writes them to the agent’s config file. The agent uses this list for fail-over protection when the primary MID/secondary MID in the list loses connection.

    When an agent detects that its IP address has changed, it automatically connects with the most efficient MID Server available from the agent's list of MID Servers.

    To secure communication between the MID Server and the agent, use the MID Server's unified key store. For details on using the MID Server unified key store, see MID Server unified key store.