There are a bunch of things to test/check/keep in mind when it comes to the upgrade to Varnish 4. Let's collect them in this subtask.
[ ] figure out if varnish4 still has the problem that old VCL shared object continue to consume memory
[ ] remember to use std.ip() instead of ipcast.ip() while porting VCL code
[ ] check if varnishlog and varnishncsa are properly started by puppet
[ ] vmod-tbf sucked at startup time: "at daemon start, everyone's already at the limit". fix the module code and/or our parameter input to make sure we err on the lax side with ratelimits on fresh start
[ ] figure out how to make sure vmod-tbf deallocates the ip db memory on VCL reload
[ ] check for threads_failed. Set thread_pool_add_delay (now in floating-point seconds) if it grows too much
[ ] vslp has no per-backend weighting. We can't assume we won't need differential weighting of hardware generations so it might be necessary to add backend weighting as a feature to libvmod-vslp