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Vladimir Dementyev
Evil Martians
Untangling Cables &
Demystifying Twisted Transistors
2023
1. It's Rails
2. Freak on a Cable
3. Y'all Want a Stream
4. Make Me ping
5. Wire Tongue
6. Threaded Transistor
7. Throw me & Forget
8. Turbo Streams Everywhere
9. (Not) Alone I Reconnect
Bonus: See You on the Other Cable
Lyrics by Vladimir "Palkan" Dementyev
Produced by Evil Martians, inc.
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1. It's Rails
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Rails is a
software
development
philosophy
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palkan
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Conceptual
Compression
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palkan
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Unboxing time!
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palkan
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Unboxing time!
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palkan
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2. Freak on a Cable
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No content
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github.com/palkan
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github.com/palkan
evilmartians.com
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github.com/palkan
evilmartians.com
anycable.io
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The Book on
abstraction
layers from and
for Rails
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palkan
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3. Y'all Want a Stream
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Channels Layer
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class ChatChannel < ApplicationCable::Channel
def subscribed
@room = Room.find_by(id: params[:id])
return reject unless @room
stream_for @room
end
def speak(data)
broadcast_to(@room,
event: "newMessage", user_id: user.id, body: data.fetch("body")
)
end
end
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class ChatChannel < ApplicationCable::Channel
def subscribed
@room = Room.find_by(id: params[:id])
return reject unless @room
stream_for @room
end
def speak(data)
broadcast_to(@room,
event: "newMessage", user_id: user.id,
body: data.fetch("body")
)
end
end
import { createConsumer } from "@rails/actioncable"
let cable = createConsumer()
let sub = cable.subscriptions.create(
{channel: "ChatChannel", id: 2023},
{
received({user_id, body}) {
console.log(`Message from ${user_id}:${body}`);
}
}
)
sub.perform("speak", {body: "Hoi!"})
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palkan_tula
palkan
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Protocol
Web
Server
Action Cable
Server
I/O
loop
Rails
Executor
Connection
Channel
Pub/Sub
Subscriber
Map
Client
Socket
Consumer
Web
Socket
Sub
Pubsub
Adapter
Monitor
Channel Channel
Worker Pool
Internal Pool
Sub Sub
Map of
Action Cable
HTTP
rack.hijack
#connect
#subscribed
{ command: "subscribe" }
OPEN
{ command: "message" }
#receive
CLOSE
#disconnect
#unsubscribed
#stream_from
#subscribe
#unsubscribe
broadcast
#invoke_callback
#send
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4. Make Me Ping
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palkan_tula
palkan
@rails/actioncable
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import { createConsumer } from "@rails/actioncable"
let cable = createConsumer()
cable.subscriptions.create(
{channel: "ChatChannel", id: 2023},
{
received({user_id, body}) {
console.log(`Message from ${user_id}:${body}`);
}
}
)
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palkan_tula
palkan
@rails/actioncable
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import { createConsumer } from "@rails/actioncable"
let cable = createConsumer()
cable.subscriptions.create(
{channel: "ChatChannel", id: 2023},
{
received({user_id, body}) {
console.log(`Message from ${user_id}:${body}`);
}
}
)
~ WebSocket connection
Abstraction to subscribe for
and receive updates
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palkan
One consumer per session (e.g., a
browser tab)
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@rails/actioncable
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github.com/le0pard/cable-shared-worker
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palkan
One consumer per session (e.g., a
browser tab)
Many subscriptions per consumer
(multiplexing)
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@rails/actioncable
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One consumer per session (e.g., a
browser tab)
Many subscriptions per consumer
(multiplexing) — how many?
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@rails/actioncable
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We may* have
as many
subscriptions
as canals in
Amsterdam
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* Doesn't mean we should though
Consumer
Monitor
Sub Sub Sub
Web
Socket
Sub Sub
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palkan_tula
palkan
@rails/actioncable
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import { createConsumer } from "@rails/actioncable"
let cable = createConsumer()
let a = cable.subscriptions.create("UserChannel") // SUBSCRIBE
let b = cable.subscriptions.create("UserChannel") //
a.unsubscribe() //
b.unsubscribe() // UNSUBSCRIBE
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palkan_tula
palkan
One consumer per session (e.g., a
browser tab)
Many subscriptions per consumer
Monitor to keep consumer connected
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@rails/actioncable
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Keep alive
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Consumer
Monitor
Web
Socket
stale timer
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palkan
Keep alive
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Consumer
Monitor
Web
Socket
ping
stale timer
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palkan_tula
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Keep alive
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Consumer
Monitor
Web
Socket
stale timer reconnect
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palkan_tula
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Action Cable Pings
Help to identify broken TCP connections
(from both sides, but not always)
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palkan_tula
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Action Cable Pings
Help to identify broken TCP connections
(from both sides, but not always)
Hardly configurable (and may be too
frequent to cause battery drain for mobile
devices)
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# config/application.rb
# Re-define internal constant
module ActionCable::Server::Connections
BEAT_INTERVAL = 10
end
import { ConnetionMonitor } from "@rails/actioncable"
// Adjust stale timeout (2xBEAT_INTERVAL)
ConnectionMonitor.staleThreshold = 20
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palkan_tula
palkan
More clients
github.com/anycable/anycable-client
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palkan_tula
palkan
More clients
github.com/anycable/anycable-client
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5. Wire Tongue
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Protocol is a
language in
which the
server and
client speak to
each other
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Protocol
Web Server
Consumer
Web
Socket
HTTP
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palkan_tula
palkan
docs.anycable.io
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{
"command":"subscribe",
"identifier":"{\"channel\" \"UserChannel\"}"
}
{
"command":"message",
"identifier":"{\"channel\":\"UserChannel\"}",
"data":"{\"action\":\"speak\",\"text\":\"hoi\"}"
}
{
"command":"unsubscribe",
"identifier":"{\"channel\":\"UserChannel\"}"
}
{"type":"welcome"}
{
"type":"confirm_subscription",
"identifier":"{\"channel\":\"UserChannel\"}"
}
{
"type":"reject_subscription",
"identifier":"{\"channel\":\"UserChannel\"}"
}
{
"identifier":"{\"channel\":\"UserChannel\"}",
"message":"{\"text\":\"hoi\"}"
}
{"type":"ping"}
{
"type":"disconnect",
"reason":"unauthorized",
"reconnect":false
}
No type!
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palkan_tula
palkan
Protocol is incomplete
No IDs (session, message)
No perform ACKs
No error handling
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palkan_tula
palkan
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let cable = createConsumer()
for(let i=0; i<10; i++) {
let sub = cable.subscriptions.create("UserChannel")
sub.unsubscribe()
}
// Will I be subscribed or not?
cable.subscriptions.create("UserChannel")
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palkan_tula
palkan
github.com/palkan/wsdirector
- loop:
multiplier: 10
actions:
- send:
data: &sub
command: "subscribe"
identifier: "{\"channel\":\"BenchmarkChannel\"}"
- send:
data:
command: "unsubscribe"
identifier: "{\"channel\":\"BenchmarkChannel\"}"
- send:
<<: *sub
- send:
data:
command: "message"
identifier: "{\"channel\":\"BenchmarkChannel\"}"
data: "{\"action\":\"echo\",\"test\":42}"
- receive:
data:
identifier: "{\"channel\":\"BenchmarkChannel\"}"
message: {action: "echo", test: 42}
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RuntimeError - Unable to find subscription with identifier: {"channel":"BenchmarkChannel"}
RuntimeError - Already subscribed to {"channel":"BenchmarkChannel"}
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palkan_tula
palkan
Solution?
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38
(First rows only note) Some random Rails application
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palkan_tula
palkan
39
let cable = createConsumer()
for(let i=0; i<10; i++) {
let sub = cable.subscriptions.create("UserChannel")
sub.unsubscribe()
}
// Will I be subscribed or not? It depends. Why so?
cable.subscriptions.create("UserChannel")
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6. Threaded Transistor
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palkan_tula
palkan
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Web
Server
Web
Socket
HTTP
Action Cable
Executor
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palkan_tula
palkan
41
Web
Server
Action Cable
Server
Web
Socket
HTTP
rack.hijack
Action Cable
Executor
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palkan_tula
palkan
41
Web
Server
Action Cable
Server
I/O
loop
Client
Socket
Web
Socket
HTTP
rack.hijack
Action Cable
Executor
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palkan_tula
palkan
41
Web
Server
Action Cable
Server
I/O
loop
Client
Socket
Web
Socket
Worker Pool
HTTP
rack.hijack
OPEN
Action Cable
Executor
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palkan_tula
palkan
41
Web
Server
Action Cable
Server
I/O
loop
Rails
Executor
Client
Socket
Web
Socket
Worker Pool
HTTP
rack.hijack
OPEN
Action Cable
Executor
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palkan_tula
palkan
41
Web
Server
Action Cable
Server
I/O
loop
Rails
Executor
Connection
Client
Socket
Web
Socket
Worker Pool
HTTP
rack.hijack
#connect
OPEN
Action Cable
Executor
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palkan_tula
palkan
41
Web
Server
Action Cable
Server
I/O
loop
Rails
Executor
Connection
Channel
Client
Socket
Web
Socket
Worker Pool
HTTP
rack.hijack
#connect
{command: "subscribe"}
OPEN
#subscribed
Action Cable
Executor
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palkan_tula
palkan
41
Web
Server
Action Cable
Server
I/O
loop
Rails
Executor
Connection
Channel
Client
Socket
Web
Socket
Worker Pool
HTTP
rack.hijack
#connect
{command: "subscribe"}
OPEN
{command: "message"}
#receive
#subscribed
Action Cable
Executor
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palkan_tula
palkan
41
Web
Server
Action Cable
Server
I/O
loop
Rails
Executor
Connection
Channel
Client
Socket
Web
Socket
Worker Pool
HTTP
rack.hijack
#connect
#unsubscribed
{command: "subscribe"}
OPEN
{command: "message"}
#receive
CLOSE
#disconnect
#subscribed
Action Cable
Executor
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palkan_tula
palkan
Action Cable Server
Thread pool executor (4 threads by default)
Must be taken into account for shared
resources (e.g., database pool)
Uses Rails executor to cleanup after work
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class Connection
identified_by :user
def connect
self.user = find_verified_user
Current.account = user.account
end
end
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class Connection
identified_by :user
def connect
self.user = find_verified_user
# BAD — will be reset at the end
# of the #handle_open call
Current.account = user.account
end
end
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class Connection
identified_by :user
before_command do
# GOOD — set for every command
Current.account = user.account
end
def connect
self.user = find_verified_user
end
end
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class Connection
identified_by :user
def connect
self.user = find_verified_user
# BAD — will be reset at the end
# of the #handle_open call
Current.account = user.account
end
end
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palkan_tula
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Units of Work
Lifecycle callbacks (connect, disconnect)
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palkan_tula
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Units of Work
Lifecycle callbacks (connect, disconnect)
Incoming commands
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palkan_tula
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Units of Work
Lifecycle callbacks (connect, disconnect)
Incoming commands
Outgoing messages
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7. Throw me & Forget
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palkan_tula
palkan
47
Rails
Executor
Connection
Pub/Sub
Subscriber
Map Client
Socket
Pubsub
Adapter
Channel
Worker Pool
Internal Pool
Pub/Sub
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palkan_tula
palkan
47
Rails
Executor
Connection
Pub/Sub
Subscriber
Map Client
Socket
Pubsub
Adapter
Channel
Worker Pool
Internal Pool
broadcast message
Pub/Sub
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palkan_tula
palkan
47
Rails
Executor
Connection
Pub/Sub
Subscriber
Map Client
Socket
Pubsub
Adapter
Channel
Worker Pool
Internal Pool
broadcast message
#broadcast
Pub/Sub
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palkan_tula
palkan
47
Rails
Executor
Connection
Pub/Sub
Subscriber
Map Client
Socket
Pubsub
Adapter
Channel
Worker Pool
Internal Pool
broadcast message
#invoke_callback
#broadcast
Pub/Sub
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palkan_tula
palkan
47
Rails
Executor
Connection
Pub/Sub
Subscriber
Map Client
Socket
Pubsub
Adapter
Channel
Worker Pool
Internal Pool
broadcast message
#invoke_callback
#broadcast
#stream_from callback
is executed
Pub/Sub
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palkan_tula
palkan
47
Rails
Executor
Connection
Pub/Sub
Subscriber
Map Client
Socket
Pubsub
Adapter
Channel
Worker Pool
Internal Pool
broadcast message
#invoke_callback
#send
#broadcast
#transmit
#stream_from callback
is executed
Pub/Sub
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palkan_tula
palkan
47
Rails
Executor
Connection
Pub/Sub
Subscriber
Map Client
Socket
Pubsub
Adapter
Channel
Worker Pool
Internal Pool
Pub/Sub
at-most once
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The pitfalls of realtime-ification, RailsConf, 2022
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palkan_tula
palkan
Yet Another Pitfall
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100.times {
ActionCable.server.broadcast "test", {text: "Count: #{_1}"}
}
# Will a client receive 1,2,3,4,...,99 in order?
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And One More
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def subscribed
stream_from "test"
# Q: Will this client receive the message?
ActionCable.server.broadcast "test", {text: "Welkom!"}
end
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Are you tired of
threads?
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palkan
I am
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8. Turbo Streams Everywhere
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palkan_tula
palkan
Turbo Streams z
Automatic subscriptions via HTML
()
Built-in Turbo::StreamsChannel
Zero application code to connect cables
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palkan_tula
palkan
Turbo Streams
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www.my-hot.app
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palkan_tula
palkan
Turbo Streams
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www.my-hot.app
SUBSCRIBE
Connection
Channel
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palkan_tula
palkan
DOM
update
Turbo Streams
54
www.my-hot.app
HTML
Action Cable broadcast
from anywhere
Connection
Channel
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palkan_tula
palkan
UNSUBSCRIBE
Turbo Streams
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www.my-hot.app
Connection
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palkan_tula
palkan
Turbo Streams
Prone to subscribe/unsubscribe race
conditions
Managed in a decentralized way (via
HTML partials)
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anycable.substack.com
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9. (Not) Alone I ReConnect
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palkan_tula
palkan
Server Restart
N clients re-connect
N clients re-subscribe each to M channels each
Threaded executor's work queue is:
(N+1)*M
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palkan_tula
palkan
Server Restart
Threaded executor's work queue is:
(N+1)*M
Server can not keep up with confirmations,
clients re-issue subscribe commands—!
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palkan_tula
palkan
Server Restart
Threaded executor's work queue is:
(N+1)*M
Server can not keep up with confirmations,
clients re-issue subscribe commands—!
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Thundering
Herd
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palkan_tula
palkan
Server Restart
Threaded executor's work queue is:
(N+1)*M
Server can not keep up with confirmations,
clients re-issue subscribe commands—!
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Connection
Avalanche
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Connection
avalanches lead
to significant
load spikes
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palkan
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How to protect
Rails from
connection
avalanches?
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palkan
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palkan_tula
palkan
Avalanche Protection
Reconnect with backoff & jitter
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palkan_tula
palkan
Avalanche Protection
Reconnect with backoff & jitter
Merge subscriptions
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palkan_tula
palkan
Avalanche Protection
Reconnect with backoff & jitter
Merge subscriptions
Avoid slow calls in #subscribed
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palkan_tula
palkan
Avalanche Protection
Reconnect with backoff & jitter
Merge subscriptions
Avoid slow calls in #subscribed
Serialize subscribe commands
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palkan_tula
palkan
68
import { createCable } from "@anycable/web"
let cable = createCable({
concurrentSubscribes: false
})
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palkan_tula
palkan
Isolate WebSocket and regular HTTP
clusters
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Avalanche Protection
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palkan_tula
palkan
Isolate WebSocket and regular HTTP
clusters
AnyCable: disconnect-less deploys
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Avalanche Protection
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palkan_tula
palkan
Isolate WebSocket and regular HTTP
clusters
AnyCable: disconnect-less deploys
AnyCable: resumable sessions
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Avalanche Protection
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See you on the other Cable
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palkan_tula
palkan
71
Map of
AnyCable
Protocol+
AnyCable-Go
I/O
poll
Rails
Executor
Connection
Channel
Cache
Session
Cable
Web
Socket
Channel
Monitor
Goroutine Pools
Sub
HTTP
#connect
#subscribed
#disconnect
#unsubscribed
broadcast
Encoder
Transport
Hub
Sub
Channel
Channel
Logger
gRPC Pool
RPC
Controller
Read Chan
Write Chan
Broadcaster
Broker
Hub
Pub/Sub
Shard
Shard
subscribe
OPEN
DATA
CLOSE
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Thank You
Slides: evilmartians.com/events
Twitter: @palkan_tula, @evilmartians,
@any_cable