Prototype local and cloud flow in Lua

--
-- Broker peering simulation (part 2)
-- Prototypes the request-reply flow
--
-- While this example runs in a single process, that is just to make
-- it easier to start and stop the example. Each thread has its own
-- context and conceptually acts as a separate process.
--
-- Author: Robert G. Jakabosky <moc.mlaerderahs|ybbob#moc.mlaerderahs|ybbob>
--

require"zmq"
require"zmq.poller"
require"zmq.threads"
require"zmsg"

local tremove = table.remove

local NBR_CLIENTS = 10
local NBR_WORKERS = 3

local pre_code = [[
local self, seed = …
local zmq = require"zmq"
local zmsg = require"zmsg"
require"zhelpers"
math.randomseed(seed)
local context = zmq.init(1)

]]

-- Request-reply client using REQ socket
--
local client_task = pre_code .. [[
local client = context:socket(zmq.REQ)
local endpoint = string.format("ipc://%s-localfe.ipc", self)
assert(client:connect(endpoint))

while true do
-- Send request, get reply
local msg = zmsg.new ("HELLO")
msg:send(client)
msg = zmsg.recv (client)
printf ("I: client status: %s\n", msg:body())
end
-- We never get here but if we did, this is how we'd exit cleanly
client:close()
context:term()
]]

-- Worker using REQ socket to do LRU routing
--
local worker_task = pre_code .. [[
local worker = context:socket(zmq.REQ)
local endpoint = string.format("ipc://%s-localbe.ipc", self)
assert(worker:connect(endpoint))

-- Tell broker we're ready for work
local msg = zmsg.new ("READY")
msg:send(worker)

while true do
msg = zmsg.recv (worker)
-- Do some 'work'
s_sleep (1000)
msg:body_fmt("OK - %04x", randof (0x10000))
msg:send(worker)
end
-- We never get here but if we did, this is how we'd exit cleanly
worker:close()
context:term()
]]

-- First argument is this broker's name
-- Other arguments are our peers' names
--
s_version_assert (2, 1)
if (#arg < 1) then
printf ("syntax: peering2 me doyouend…\n")
os.exit(-1)
end
-- Our own name; in practice this'd be configured per node
local self = arg[1]
printf ("I: preparing broker at %s…\n", self)
math.randomseed(os.time())

-- Prepare our context and sockets
local context = zmq.init(1)

-- Bind cloud frontend to endpoint
local cloudfe = context:socket(zmq.ROUTER)
local endpoint = string.format("ipc://%s-cloud.ipc", self)
cloudfe:setopt(zmq.IDENTITY, self)
assert(cloudfe:bind(endpoint))

-- Connect cloud backend to all peers
local cloudbe = context:socket(zmq.ROUTER)
cloudbe:setopt(zmq.IDENTITY, self)

local peers = {}
for n=2,#arg do
local peer = arg[n]
-- add peer name to peers list.
peers[#peers + 1] = peer
peers[peer] = true -- map peer's name to 'true' for fast lookup
printf ("I: connecting to cloud frontend at '%s'\n", peer)
local endpoint = string.format("ipc://%s-cloud.ipc", peer)
assert(cloudbe:connect(endpoint))
end
-- Prepare local frontend and backend
local localfe = context:socket(zmq.ROUTER)
local endpoint = string.format("ipc://%s-localfe.ipc", self)
assert(localfe:bind(endpoint))

local localbe = context:socket(zmq.ROUTER)
local endpoint = string.format("ipc://%s-localbe.ipc", self)
assert(localbe:bind(endpoint))

-- Get user to tell us when we can start…
printf ("Press Enter when all brokers are started: ")
io.read('*l')

-- Start local workers
local workers = {}
for n=1,NBR_WORKERS do
local seed = os.time() + math.random()
workers[n] = zmq.threads.runstring(nil, worker_task, self, seed)
workers[n]:start(true)
end
-- Start local clients
local clients = {}
for n=1,NBR_CLIENTS do
local seed = os.time() + math.random()
clients[n] = zmq.threads.runstring(nil, client_task, self, seed)
clients[n]:start(true)
end

-- Interesting part
-- -------------------------------------------------------------
-- Request-reply flow
-- - Poll backends and process local/cloud replies
-- - While worker available, route localfe to local or cloud

-- Queue of available workers
local worker_queue = {}
local backends = zmq.poller(2)

local function send_reply(msg)
local address = msg:address()
-- Route reply to cloud if it's addressed to a broker
if peers[address] then
msg:send(cloudfe) -- reply is for a peer.
else
msg:send(localfe) -- reply is for a local client.
end
end

backends:add(localbe, zmq.POLLIN, function()
local msg = zmsg.recv(localbe)

-- Use worker address for LRU routing
worker_queue[#worker_queue + 1] = msg:unwrap()
-- if reply is not "READY" then route reply back to client.
if (msg:address() ~= "READY") then
send_reply(msg)
end
end)

backends:add(cloudbe, zmq.POLLIN, function()
local msg = zmsg.recv(cloudbe)
-- We don't use peer broker address for anything
msg:unwrap()
-- send reply back to client.
send_reply(msg)
end)

local frontends = zmq.poller(2)
local localfe_ready = false
local cloudfe_ready = false

frontends:add(localfe, zmq.POLLIN, function() localfe_ready = true end)
frontends:add(cloudfe, zmq.POLLIN, function() cloudfe_ready = true end)

while true do
local timeout = (#worker_queue > 0) and 1000000 or -1
-- If we have no workers anyhow, wait indefinitely
rc = backends:poll(timeout)
assert (rc >= 0)

-- Now route as many clients requests as we can handle
--
while (#worker_queue > 0) do
rc = frontends:poll(0)
assert (rc >= 0)
local reroutable = false
local msg
-- We'll do peer brokers first, to prevent starvation
if (cloudfe_ready) then
cloudfe_ready = false -- reset flag
msg = zmsg.recv (cloudfe)
reroutable = false
elseif (localfe_ready) then
localfe_ready = false -- reset flag
msg = zmsg.recv (localfe)
reroutable = true
else
break; -- No work, go back to backends
end

-- If reroutable, send to cloud 20% of the time
-- Here we'd normally use cloud status information
--
local percent = randof (5)
if (reroutable and #peers > 0 and percent == 0) then
-- Route to random broker peer
local random_peer = randof (#peers) + 1
msg:wrap(peers[random_peer], nil)
msg:send(cloudbe)
else
-- Dequeue and drop the next worker address
local worker = tremove(worker_queue, 1)
msg:wrap(worker, "")
msg:send(localbe)
end
end
end
-- We never get here but clean up anyhow
localbe:close()
cloudbe:close()
localfe:close()
cloudfe:close()
context:term()