We have randomly seen Cookbook dependency resolution error while using knife ssh with -C. Is it that the issue occurs when we have concurrency set to a high number? If so, how do we find the optimal value of C.
There's no hard and fast rule; the amount of work Chef Server has to do to solve your dependencies changes based on how you use it. If you use environments to lock down your cookbooks to exact versions, the amount of work required will be a lot less.
Chef Server maintains a pool of dependency solver processes, so another thing you can do is increase the number of workers. See opscode_erchef['depsolver_worker_count'] in chef-server.rb Optional Settings for more info.
Any pointers?