SFTP service went down intermittently on API Gateway

Products

• CA API Gateway
• API SECURITY
• CA API Gateway Precision API Monitoring Module for API Gateway (Layer 7)
• CA API Gateway Enterprise Service Manager (Layer 7)
• STARTER PACK-7
• CA Microgateway

Issue/Introduction

When the sftp traffic is high, the sftp service stop working intermitterntly.

From the ssg log, there is exception as below,

2020-07-27T22:15:28.023-0400 SEVERE  1667 com.l7tech.external.assertions.ssh.server.ae: Exception caught in SFTP subsystem
java.util.concurrent.RejectedExecutionException: Task [email protected] rejected from [email protected][Running, pool size = 20, active threads = 20, queued tasks = 25, completed tasks = 118]

The FTP client has error message like "Too many concurrent connections",

Cause

The gateway has default limit as 20 for the concurrent SFTP download threads

Environment

Release : 9.4

Component : API GTW ENTERPRISE MANAGER

Resolution

Increase the value of following cluster wide property as per the requirement of the current traffic, for example, set it as 50,

ssh.responseDownloadThreadLimit

It's a hidden cwp, on cluster wide properties window, click Add button, manually input the above cwp, it will show the default value as below,