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When I launch new task (Spring Batch Job) using Spring Cloud Data Flow, I see that SCDF auto initialize Tomcat with some "random" ports but I do not know if there ports are created randomly or following any rule of the framework?

Therefore, I sometime have a trouble that "Web server failed to start. Port 123456 was already in use".

In conclusion, my questions are:
1) How does the framework choose ports for initializing? (randomly or by principle)?
2) Are there anyway to launch task effectively without duplicated ports(fixed configuration or method for choosing unused port at particular time)?

DM CHAU
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I don't think SCDF has anything to do with the port assignment etc.,

It is your task application that gets launched. You need to decide whether you really need the web dependency that brings in the tomcat to your application.

Assuming you use Spring Boot, you can either exclude the web starter dependency in your dependencies or pass the command line arg server.port=<?> to a specific port when launching the task (if you really need this task app to be a web app).

Ilayaperumal Gopinathan
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  • so you mean that if I use spring-boot-starter-web in my pom.xml, I should set server.port in my application.properties? The second question is that if my jar has multiple tasks, how can I set multiple server.port (For example: I have batch job A,B and C in my jar so when I deployed it into SCDF it would be 3 separated tasks. How could I configure port for this situation). – DM CHAU May 05 '20 at 10:59
  • Unless you have a specific requirement, It is not a good practice to have multiple tasks inside the same jar. You might want to register those task apps as separate ones and invoke them. Otherwise, you need to programmatically handle the way you can set the `server.port` to each task based on which gets triggered. – Ilayaperumal Gopinathan May 05 '20 at 11:25
  • and If I do not use web starter dependency in my pom, Spring would not initialize port automatically? – DM CHAU May 06 '20 at 02:52