That is the task history. A limited number of previous containers are kept when you update a service. You can delete them with docker container rm or run docker swarm update --task-history-limit 0 to disable this funtionality. The next update will then remove the old containers. But I think it can be useful when you update a service and something goes wrong. You can roll back and keep not just the previous configuration but the previous container. The stopped container will run again and the new version will be stopped.
ta@ta-mb ~
» docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
044a16fcf4b0 httpd:2.4 "httpd-foreground" About a minute ago Up About a minute 80/tcp httpd.1.m9hc3a4r5xi2m01s4sl7d00ig
0f054bca58d1 httpd:2.4 "httpd-foreground" 8 minutes ago Exited (0) About a minute ago httpd.1.f3xlnlnqg095zpus6rzs9vyzh
ta@ta-mb ~
» docker service rollback httpd
httpd
rollback: manually requested rollback
overall progress: rolling back update: 1 out of 1 tasks
1/1: running [> ]
verify: Service converged
ta@ta-mb ~
» docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
c05d2205173d httpd:2.4 "httpd-foreground" 12 seconds ago Up 7 seconds 80/tcp httpd.1.55m1syhjrc9bx16ja3urosvue
044a16fcf4b0 httpd:2.4 "httpd-foreground" 2 minutes ago Exited (0) 8 seconds ago httpd.1.m9hc3a4r5xi2m01s4sl7d00ig
ta@ta-mb ~
» docker service rollback httpd
httpd
rollback: manually requested rollback
overall progress: rolling back update: 1 out of 1 tasks
1/1: running [> ]
verify: Service converged
ta@ta-mb ~
» docker ps -a
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
1b5f100d870e httpd:2.4 "httpd-foreground" 15 seconds ago Up 9 seconds 80/tcp httpd.1.i672ukc53x3pnvkfscr4fyq84
c05d2205173d httpd:2.4 "httpd-foreground" About a minute ago Exited (0) 10 seconds ago httpd.1.55m1syhjrc9bx16ja3urosvue
PS.: Since I finally understand what you wanted to know, I changed the topic title. Please don’t create a topic with such a general title that doesn’t say anithing about your problem.