Kong: worker processes each hold their own Lua state

# kong.conf
nginx_worker_processes = auto      # one per CPU core

-- per worker, not per node
local counter = 0

-- per node, shared across workers
local shm = ngx.shared.kong
local n = shm:incr("hits", 1, 0)

-- per request, and correctly isolated
kong.ctx.plugin.started_at = ngx.now()

# 8 workers, module-level counter:
#   1, 1, 1, 2, 1, 2, ...   requests land on different workers
#
# ngx.shared.kong:incr:
#   1, 2, 3, 4, 5, ...      the node total
#
# This is also why the rate-limiting plugin's local policy is per node, and
# why cache invalidation between nodes needs the cluster events mechanism.