The Route via SSH2 assertion is used to secure requests from the Gateway to backend services to provide SCP and SFTP (SSH File Transfer Protocol) support for the Gateway, so that SCP and SFTP outbound requests can be made to an external SSH server.
The SFTP access through "List via SFTP" or "Get via SFTP" failed with such error message as:
SSH routing error: Failed to retrieve ssh session: Pool exhausted
These assertions can be created by the Route via SSH2 assertion.
The cluster wide property ssh.session.pool.maxActive defines the maximum number of sessions (per key) that can be allocated by the pool (checked out to client threads) at one time (Default: 10).
After the maximum number of sessions is reached, the session pool is exhausted, and the assertion fails.
To resolve the problem, increase the value of the property ssh.session.pool.maxActive.
Regarding the cluster wide property ssh.session.pool.maxActive, see the docops for detail.