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 java.util.concurrent.FutureTask@45c1b467 rejected from com.l7tech.util.c6@3ea5c0c[Running, pool size = 20, active threads = 20, queued tasks = 25, completed tasks = 118]

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

Environment

Release : 9.4

Component : API GTW ENTERPRISE MANAGER

Cause

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

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,