Answer
- Select all the circles
- Copy > Paste in Front Cmd + F Mac or Ctrl + F Win
- Fill color = none
- Stroke = 100% black, aligned outside and the same size as the separation from the green circles
- Menu Object > Expand
- Pathfinder > Unite
- Menu Object > Compound Shape > Release
- Menu Object > Ungroup
- Delete the inner shapes and keep the exterior shape
- Fill color = none
- Set the stroke width and type dashed
- Menu Effect > Stylize > Round corners
Attribution
Source : Link , Question Author : jsevic , Answer Author : Community