External Server Coasting
When a server deployed by an ICE Agent loses its connection, the default behavior is to halt all operation and wait for the connection to return. This default behavior can be changed to External Server Coasting.
Coasting means that the server continues to operate in the configuration it had prior to losing its connection with the ICE Server. External Server Coasting keeps gateways and other external servers functioning while network connectivity to ICE Server is severed. This feature is intended for use in environments where external server components are likely to lose their network connectivity to the ICE Server for long periods of time.
The use of Coast Mode is not recommended in most environments.
To enable External Server Coasting
Use the --coast command when launching an ICE Agent component. For example:agent external patch –-coast
agent external rallypoint --coast
agent external reflector --coast
When an ICE Agent launches a component with the --coast command, it will continue operating when disconnected and reconnect when possible. The disconnection and reconnection sections below cover the exact behavior. At least one initial connection with the ICE Server is required to enable coasting.
Note: External Archiver Servers do not support Coasting.
Do not use agent external archiver –coast.
Do not use agent external archiver –coast.
Terms to Know:
The following terms are used below and defined here for reference.
Active Server: The server in the Group performing the function of the server, also known as the “leader”. For example: , patching, reflecting, archiving, etc.).Standby Servers: Any other server in the Group that is participating in voting, but not performing the action of the group.Special considerations when using coast mode
When a server is coasting, it operates without communicating with its ICE Server. Consider these limitations and risks:
External servers elect a Leader from available Group members but cannot operate in the last-provisioned state if they can't achieve quorum. They can coast disconnected from the ICE Server but not from Rallypoints or IGMP multicast groups used for leader election.Coasting servers lower their priority in leader elections, allowing connected members to take leadership. Leadership changes cause brief service outages (~30 seconds).All external servers in a Group must use coasting. Mixed configurations may cause system issues.Do not modify election configuration or add/delete servers while coasting to avoid failures and audio loops. Configuration changes made on the ICE Server cannot be received by coasting servers until they reconnect.Coasting servers can't report status to ICE Server, leading to possible confusion about system state.Due to the reasons listed above, the use of Coast Mode is discouraged except in very specific environments where its benefits outweigh these concerns.
Reconnection to ICE Server while Coasting
When a coasting server is able to restore its connection to ICE Server, it will synchronize its state with the ICE Server. The external server will apply any server-side configuration changes to its currently provisioned state and stores that configuration for use during any subsequent outages.
Restarting a Coasting Agent Server
If a coasting ICE Agent server needs to be restarted, and the ICE Server is unreachable when it restarts, the coasting server will start and run in its last-known state. This state is obtained using connection data from the ICE Server during the last connection.
If the ICE Server is up, the coasting server will reconnect as normal and then update its connection data for any future disconnections.
New Coasting Servers During Disconnection
If a server has never been launched in coast mode, then there will be no last-known state to use. Because of this, you will not be able to successfully launch new server components in coast mode if they cannot establish a connection to the ICE Server during startup.
Monitoring Coasting
When using --coast the agent will also issue coast status messages to the log. For example:
CoastMonitor | System is coasting. Agent will continue to operate in its last-provisioned state.
and
CoastMonitor | Reconnected to ICE Server. Resuming normal operation.