Building, Deploying, and Monitoring Ruby Web Applications with Falcon (Kaigi on Rails 2025)

#write #wait Thread #join Thread::Mutex #lock Thread::Queue #pop Addrinfo .getaddrinfo Process .wait Timeout .timeout Fiber#raise Error Handling Fiber#storage “Per-request” State Management IO::Buffer Zero-copy Memory I/O Native Coroutines (Also used for M:N threading) IO#timeout Safety Net

Async::Queue Async::Barrier Async::Semaphore Async::Task Async::Scheduler Async::Condition Async::HTTP Protocol::HTTP Async::Service

Protocol::Rack Rack 1, 2 & 3 Compatibility

Application ActiveSupport IsolatedExecutionState = : fi ber ActiveRecord #lease_connection ActionDispatch

Streaming Response ActionCable Server Adapterization Async::Cable Async::WebSocket Async::Job Async::Redis Live

None

rails new myproject

bundle remove puma bundle add falcon

bin/rails s

= > Booting Falcon v0.52.0 = > Rails 8.0.2 application

sta r ting in development http: / / localhost:3000 = > Run `bin/ r ails se r ve r - - help` fo r mo r e sta r tup options

None

Stuck on HTTP/1.1… 㠡ࡏ HTTP/1 ⋯ ⋯

falcon serve

Defaults to HTTP/2 with TLS. σϑΥϧτͰTLS෇͖HTTP/2Λ࠾༻͍ͯ͠·͢ɻ

HTTP/2 in the browser requires TLS. ϒϥ΢βͰͷHTTP/2ར༻ʹ͸TLS͕ඞਢͰ͢ɻ

Develop the way you deploy. σϓϩΠ͢ΔΑ͏ʹ։ൃ͢Δɻ

None

The Localhost gem provides self-signed certi fi cates. Localhost gem͸ࣗݾॺ໊ূ໌ॻΛఏڙ͠·͢ɻ

bake localhost:install

None

Also works on Linux. LinuxͰ΋ಈ࡞͠·͢ɻ

✅ HTTP/2 + TLS

ActiveRecord

Falcon is extremely good at non-blocking I/O. Falcon͸ϊϯϒϩοΩϯάI/Oʹඇৗʹ༏Ε͍ͯ·͢ɻ

Rails still defaults to thread per request. Rails͸ґવͱͯ͠ϦΫΤετ͝ͱʹεϨουΛׂΓ౰ͯΔํࣜ ͕σϑΥϧτͰ͢ɻ

# conf i g/application. r b conf i g.active_ r

eco r d.pe r manent_connection_checkout = :disallowed conf i g.active_suppo r t.isolation_level = :f i be r # O r di r ectly if not pa r t of a Rails application: ActiveReco r d.pe r manent_connection_checkout = :disallowed ActiveSuppo r t : : IsolatedExecutionState.isolation_level = :f i be r

# conf i g/application. r b conf i g.active_ r

Everything just works on Rails 8+ Rails 8Ҏ߱Ͱ͸͢΂ͯͦͷ··ಈ࡞͠·͢ɻ

class Pizza < ActiveReco r d : : Base validates

:name, p r esence: t r ue def cook!(du r ation = 0.001) update!(status: 'cooking') sleep(du r ation) update!(status: 'hot') end end r un do |env| r equest = Rack : : Request.new(env) pizza = Pizza.c r eate!(name: "Ma r ghe r ita", status: "cold") pizza.cook! [200, {"content - type" = > "application/json"}, [pizza.to_json]] end

class Pizza < ActiveReco r d : : Base validates

4 workers, 3 threads (recommended default) Falcon vs Puma Requests/second

0 1000 2000 3000 4000 Connection Count 1 4 40 Pum a F a lcon Pum a F a lcon Pum a F a lcon 3,232 461 166 1,231 456 165

Just increase the number of threads right? εϨου਺Λ૿΍ͤ͹͍͍͚ͩͰ͢ΑͶʁ

4 workers, 10 threads Falcon vs Puma Requests/second 0 1500

3000 4500 6000 Connection Count 40 80 160 Pum a F a lcon Pum a F a lcon Pum a F a lcon 5,341 4,779 3,232 2,214 2,241 2,223

200%+ More throughput.

✅ ActiveRecord

ActiveJob

ActiveJob works fi ne with Falcon… ActiveJob͸FalconͰ΋໰୊ͳ͘ಈ࡞͠·͢…

But existing job processors are not async-aware. ͔͠͠ɺطଘͷδϣϒϓϩηοα͸ඇಉظରԠͰ͸͋Γ·ͤΜɻ

We expect to see similar concurrency limitations. ಉ༷ͷฒߦੑͷ੍ݶ͕ݱΕΔͱ༧૝͞Ε·͢ɻ

I built Async::Job for concurrency. ฒߦॲཧͷͨΊʹAsync::JobΛ։ൃ͠·ͨ͠ɻ

Async::Job is a generic queue interface. Async::Job͸൚༻తͳΩϡʔΠϯλʔϑΣʔεͰ͢ɻ

Async::Job::Queue Job Data Job Data Enqueue Dequeue

We need wrap the queue with the interface expected by

ActiveJob. ActiveJob͕ظ଴͢ΔΠϯλʔϑΣʔεͰΩϡʔΛϥοϓ͢Δඞ ཁ͕͋Γ·͢ɻ

Async::Job::Queue Job Data Job Data Enqueue Dequeue ActiveJob Seri a

lize ActiveJob Deseri a lize Perform Now Perform L a ter

Provided by Async::Job::Adapter::ActiveJob ͜Ε͸Async::Job::Adapter::ActiveJob͕ఏڙ͠·͢ɻ

It’s a nice design because we can directly execute the

jobs. δϣϒΛ௚઀࣮ߦͰ͖ΔͷͰɺ༏Εͨઃܭʹͳ͍ͬͯ·͢ɻ

Most other adapters have “wrappers”. ଞͷ΄ͱΜͲͷΞμϓλ͸ʮϥούʔʯΛ͍࣋ͬͯ·͢ɻ

module ActiveJob module QueueAdapte r s # = Sidekiq adapte

r fo r Active Job class SidekiqAdapte r < Abst r actAdapte r def enqueue(job) # :nodoc: job.p r ovide r _job_id = JobW r appe r .set( w r apped: job.class, queue: job.queue_name ).pe r fo r m_async(job.se r ialize) end class JobW r appe r # :nodoc: include Sidekiq : : Wo r ke r def pe r fo r m(job_data) Base.execute job_data.me r ge("p r ovide r _job_id" = > jid) end end end end

module ActiveJob module QueueAdapte r s # = Sidekiq adapte

Async::Job queue adapter directly invokes ActiveJob. Async::JobͷΩϡʔΞμϓλ͸ActiveJobΛ௚઀ݺͼग़͠·͢ɻ

module Async module Job module Adapte r module ActiveJob #

An executo r fo r p r ocessing jobs using `ActiveJob`. class Executo r # Initialize the executo r with an optional delegate. def initialize(delegate = nil) @delegate = delegate end # Execute a job with the given data. # @pa r amete r job_data [Hash] Se r ialized job data f r om ActiveJob. def execute(job_data) : : ActiveJob : : Callbacks. r un_callbacks(:execute) do job = : : ActiveJob : : Base.dese r ialize(job_data) begin job.pe r fo r m_now r escue = > e r r o r r r r r r

# Initialize the executo r with an optional delegate. def

initialize(delegate = nil) @delegate = delegate end # Execute a job with the given data. # @pa r amete r job_data [Hash] Se r ialized job data f r om ActiveJob. def execute(job_data) : : ActiveJob : : Callbacks. r un_callbacks(:execute) do job = : : ActiveJob : : Base.dese r ialize(job_data) begin job.pe r fo r m_now r escue = > e r r o r # Igno r e, as ActiveJob has al r eady logged the e r r o r . end end end

# Initialize the executo r with an optional delegate. def

initialize(delegate = nil) @delegate = delegate end # Execute a job with the given data. # @pa r amete r job_data [Hash] Se r ialized job data f r om ActiveJob. def execute(job_data) : : ActiveJob : : Callbacks. r un_callbacks(:execute) do job = : : ActiveJob : : Base.dese r ialize(job_data) begin job.pe r fo r m_now r escue = > e r r o r # Igno r e, as ActiveJob has al r eady logged the e r r o r . end end end

It’s a cleaner design with less overhead. ΑΓগͳ͍ΦʔόʔϔουͰɺ͖ͬ͢Γͱͨ͠ઃܭʹͳ͍ͬͯ· ͢ɻ

bundle add \ async - job - adapter - active_job

# conf i g/initialize r s/async_job. r b Rails.application.conf i

gu r e do conf i g.async_job.def i ne_queue "default" do enqueue Async : : Job : : P r ocesso r : : Agg r egate dequeue Async : : Job : : P r ocesso r : : Redis end conf i g.async_job.def i ne_queue "local" do dequeue Async : : Job : : P r ocesso r : : Inline end end

# conf i g/initialize r s/async_job. r b Rails.application.conf i

# conf i g/application. r b conf i g.active_job.queue_adapte r

= :async_job

# conf i g/application. r b conf i g.active_job.queue_adapte r

= :async_job

class AsyncJobBenchma r kJob < ActiveJob : : Base self.queue_adapte

r = :async_job queue_as :default def pe r fo r m sleep(0.001) end end

class AsyncJobBenchma r kJob < ActiveJob : : Base self.queue_adapte

1 client, 1 worker, 1ms sleep per job. Sidekick vs

Async::Job Jobs/second 0 7500 15000 22500 30000 Enqueue Dequeue Sidekiq Async::Job Sidekiq Async::Job 6,000 28,000 4,100 22,000

(User reported comparison) SolidQueue vs Async::Job URLs cr a wled/second

0 6.5 13 19.5 26 SolidQueue Async::Job 25 8.3

I created a small demo. খ͞ͳσϞΛ࡞੒͠·ͨ͠ɻ

class JobExecution < ApplicationReco r d afte r _c r

eate_commit - > { b r oadcast_append_to "job_executions" } end

class MyJob < ApplicationJob queue_as "default" def pe r fo

r m(*a r guments) JobExecution.c r eate!(name: self.class.name, data: { a r guments: a r guments, }) end end

class HomeCont r olle r < ApplicationCont r olle r

def index @job_executions = JobExecution.all end def execute job = MyJob if queue = pa r ams[:queue] job = job.set(queue: queue) end job.pe r fo r m_late r (queued_to: queue) end end

<h1>Async Job < / h1> <p>This is a simple example

of how to use the async job gem. You can use the fo r m below to submit a job to the queue. The job will be executed in the backg r ound and the r esults will be displayed in the table below. < / p> <fo r m action="/execute" method="post"> <select name="queue"> <% Rails.application.conf i g.async_job.def i nitions.each do |name, _| %> <option value="<%= name %>"><%= name %> < / option> <% end %> < / select> <input type="submit" value="Submit" / > < / fo r m> <h2>Job Executions < / h2> <%= tu r bo_st r eam_f r om "job_executions" %> <table> <thead> r

<h1>Async Job < / h1> <p>This is a simple example

of how to use the async job gem. You can use the fo r m below to submit a job to the queue. The job will be executed in the backg r ound and the r esults will be displayed in the table below. < / p> <fo r m action="/execute" method="post"> <select name="queue"> <% Rails.application.conf i g.async_job.def i nitions.each do |name, _| %> <option value="<%= name %>"><%= name %> < / option> <% end %> < / select> <input type="submit" value="Submit" / > < / fo r m> <h2>Job Executions < / h2> <%= tu r bo_st r eam_f r om "job_executions" %> <table> <thead> r

<% end %> < / select> <input type="submit" value="Submit" /

> < / fo r m> <h2>Job Executions < / h2> <%= tu r bo_st r eam_f r om "job_executions" %> <table> <thead> <t r > <th>ID < / th> <th>Name < / th> <th>Data < / th> < / t r > < / thead> <tbody id="job_executions"> <%= r ende r @job_executions %> < / tbody> < / table>

None

Successfully upg r aded to WebSocket (REQUEST_METHOD : GET, HTTP_CONNECTION

: Upg r ade, HTTP_UPGRADE : websocket) Tu r bo : : St r eamsChannel is t r ansmitting the subsc r iption conf i r mation Tu r bo : : St r eamsChannel is st r eaming f r om job_executions

None

Successfully upg r aded to WebSocket (REQUEST_METHOD : GET, HTTP_CONNECTION

: Upg r ade, HTTP_UPGRADE : websocket) Tu r bo : : St r eamsChannel is t r ansmitting the subsc r iption conf i r mation Tu r bo : : St r eamsChannel is st r eaming f r om job_executions Sta r ted POST "/execute" fo r : : 1 at 2025-08-02 16 : 50 : 56 +1200 P r ocessing by HomeCont r olle r #execute as TURBO_STREAM Pa r amete r s: {"queue" = > "default"} [ActiveJob] Enqueued MyJob (Job ID : 069bf564-c358-4da8-b255-13be3051a112) to AsyncJob(default) with a r guments: {queued_to: "default"} [ActiveJob] ↳ app/cont r olle r s/home_cont r olle r . r b:13:in 'HomeCont r olle r #execute' No template found fo r HomeCont r olle r #execute, r ende r ing head :no_content Completed 204 No Content in 15ms (ActiveReco r d: 0.0ms (0 que r ies, 0 cached) | GC : 0.2ms) Tu r bo : : St r eamsChannel t r ansmitting "<tu r bo - st r eam action=\"append\" ta r get=\"job_executions\"><template><t r id=\"job_execution_1\">\n\t<td>1 < / td>\n\t<td>MyJob < / td>\n\t<td>{"a r guments" => [{"queued_to" => "default"}]} < / td>\n < / t r > < / template> < / tu r bo - st r eam>" (via st r eamed f r om job_executions)

Successfully upg r aded to WebSocket (REQUEST_METHOD : GET, HTTP_CONNECTION

None

✅ ActiveJob

ActionCable ͦͷσϞ͸ɺHTTP/1ʹ͔͠ରԠ͍ͯ͠ͳ͍ActionCableΛ࢖༻͠ ͍ͯ·ͨ͠…

Falcon defaults to HTTP/2… Falcon͸σϑΥϧτͰHTTP/2Λ࢖༻͠·͢…

Most browsers don’t support HTTP/2 WebSockets… ΄ͱΜͲͷϒϥ΢β͸HTTP/2ͷWebSocketΛαϙʔτ͍ͯ͠· ͤΜ…

None

F a iled:

bundle add async - cable

None

1 process, 1000 clients, 20 broadcasts. ActionCable vs Async::Cable Mess

a ges/second 0 20000 40000 60000 80000 Mess a ge ActionC a ble Async::C a ble 80,000 32,000

✅ ActionCable

Streaming

Rack 3 introduced real time streaming. Rack 3ͰϦΞϧλΠϜετϦʔϛϯά͕ಋೖ͞Ε·ͨ͠ɻ

class St r eamingCont r olle r < ApplicationCont r

olle r def st r eam body = p r oc do |st r eam| 10.downto(1) do |i| st r eam.w r ite " # { i} bottles of bee r on the wall\n" sleep 1 st r eam.w r ite " # { i} bottles of bee r \n" sleep 1 st r eam.w r ite "Take one down, pass it a r ound\n" sleep 1 st r eam.w r ite " # { i - 1} bottles of bee r on the wall\n" sleep 1 end end self. r esponse = Rack : : Response[200, {"content - type" = > "text/plain"}, body] end end

class St r eamingCont r olle r < ApplicationCont r

10 bottles of bee r on the wall 10 bottles

of bee r Take one down, pass it a r ound 9 bottles of bee r on the wall 9 bottles of bee r on the wall 9 bottles of bee r Take one down, pass it a r ound 8 bottles of bee r on the wall 8 bottles of bee r on the wall 8 bottles of bee r Take one down, pass it a r ound 7 bottles of bee r on the wall 7 bottles of bee r on the wall 7 bottles of bee r Take one down, pass it a r ound 6 bottles of bee r on the wall 6 bottles of bee r on the wall 6 bottles of bee r Take one down, pass it a r ound

Of course, that example is a bit boring… ΋ͪΖΜɺͦͷྫ͸গ͠ୀ۶Ͱ͕͢…

None

It also supports multiplayer. ϚϧνϓϨΠϠʔʹ΋ରԠ͍ͯ͠·͢ɻ

✅ Streaming

Summary Building with Falcon ✅ HTTP/2 + TLS with loc

a lhost development certi f ic a tes.

Summary Building with Falcon ✅ HTTP/2 + TLS with loc

a lhost development certi f ic a tes. ✅ ActiveRecord fully supported (in f iber mode).

Summary Building with Falcon ✅ HTTP/2 + TLS with loc

a lhost development certi f ic a tes. ✅ ActiveRecord fully supported (in f iber mode). ✅ ActiveJob with Async support using Async::Job::Ad a pter::ActiveJob.

Summary Building with Falcon ✅ HTTP/2 + TLS with loc

a lhost development certi f ic a tes. ✅ ActiveRecord fully supported (in f iber mode). ✅ ActiveJob with Async support using Async::Job::Ad a pter::ActiveJob. ✅ ActionC a ble repl a ced by Async::C a ble for improved perform a nce a nd HTTP/2 WebSockets.

Summary Building with Falcon ✅ HTTP/2 + TLS with loc

a lhost development certi f ic a tes. ✅ ActiveRecord fully supported (in f iber mode). ✅ ActiveJob with Async support using Async::Job::Ad a pter::ActiveJob. ✅ ActionC a ble repl a ced by Async::C a ble for improved perform a nce a nd HTTP/2 WebSockets. ✅ Re a l-time Stre a ming a nd Inter a ctively using R a ck 3.

2. Deploying with Falcon

falcon serve

Not designed for deployment. σϓϩΠΛ૝ఆͯ͠ઃܭ͞Ε͍ͯ·ͤΜɻ

Hard to con fi gure. ઃఆ͕೉͍͠ɻ

falcon host

falcon.rb de fi nes how to run your application. falcon.rb͸ΞϓϦέʔγϣϯͷ࣮ߦํ๏Λఆٛ͠·͢ɻ

# ! /us r /bin/env falcon - host # f

r ozen_st r ing_lite r al: t r ue r equi r e "falcon/envi r onment/ r ack" r equi r e "falcon/envi r onment/lets_enc r ypt_tls" r equi r e "falcon/envi r onment/supe r viso r " se r vice " w w w .example.com" do include Falcon : : Envi r onment : : Rack include Falcon : : Envi r onment : : LetsEnc r yptTLS end

# ! /us r /bin/env falcon - host # f

> bundle exec ./falcon. r b 0.0s info: Falcon :

: Command : : Host | Falcon Host v0.52.0 taking flight! | - Conf i gu r ation: ./falcon. r b | - To te r minate: Ct r l-C o r kill 87272 | - To r eload: kill -HUP 87272 0.07s info: Async : : Containe r : : Notify : : Console | {status: "Initializing cont r olle r . . . "} 0.07s info: Falcon : : Se r vice : : Se r ve r | Sta r ting w w w .example.com on #<Falcon : : P r oxyEndpoint p r otocol=Async : : HTTP : : P r otocol : : HTTP2 endpoint=unix:/Use r s/samuel/Develope r / socket r y/ w w w .example.com/application.ipc> 0.07s info: Async : : Se r vice : : Cont r olle r | Cont r olle r sta r ting . . . 0.58s info: Async : : Containe r : : Notify : : Console | { r eady: t r ue, size: 11} 0.59s info: Async : : Se r vice : : Cont r olle r | Cont r olle r sta r ted . . .

> bundle exec ./falcon. r b 0.0s info: Falcon :

: Command : : Host | Falcon Host v0.52.0 taking flight! | - Conf i gu r ation: ./falcon. r b | - To te r minate: Ct r l-C o r kill 87272 | - To r eload: kill -HUP 87272 0.07s info: Async : : Containe r : : Notify : : Console | {status: "Initializing cont r olle r . . . "} 0.07s info: Falcon : : Se r vice : : Se r ve r | Sta r ting w w w .example.com on #<Falcon : : P r oxyEndpoint p r otocol=Async : : HTTP : : P r otocol : : HTTP2 endpoint=unix:/Use r s/samuel/Develope r / socket r y/ w w w .example.com/application.ipc> 0.07s info: Async : : Se r vice : : Cont r olle r | Cont r olle r sta r ting . . . 0.58s info: Async : : Containe r : : Notify : : Console | { r eady: t r ue, size: 11} 0.59s info: Async : : Se r vice : : Cont r olle r | Cont r olle r sta r ted . . .

# ! /us r /bin/env falcon - host # f

r ozen_st r ing_lite r al: t r ue r equi r e "falcon/envi r onment/ r ack" r equi r e "falcon/envi r onment/lets_enc r ypt_tls" r equi r e "falcon/envi r onment/supe r viso r " se r vice " w w w .example.com" do include Falcon : : Envi r onment : : Rack po r t {ENV.fetch("PORT", 3000).to_i} endpoint {Async : : HTTP : : Endpoint.pa r se("http: / / localhost", po r t: po r t)} end

# ! /us r /bin/env falcon - host # f

r ozen_st r ing_lite r al: t r ue r equi r e "falcon/envi r onment/ r ack" r equi r e "falcon/envi r onment/lets_enc r ypt_tls" r equi r e "falcon/envi r onment/supe r viso r " se r vice " w w w .example.com" do include Falcon : : Envi r onment : : Rack po r t {ENV.fetch("PORT", 3000).to_i} endpoint {Async : : HTTP : : Endpoint.pa r se("http: / / localhost", po r t: po r t)} end

> bundle exec ./falcon. r b 0.0s info: Falcon :

: Command : : Host | Falcon Host v0.52.0 taking flight! | - Conf i gu r ation: ./falcon. r b | - To te r minate: Ct r l-C o r kill 87577 | - To r eload: kill -HUP 87577 0.07s info: Async : : Containe r : : Notify : : Console | {status: "Initializing cont r olle r . . . "} 0.07s info: Falcon : : Se r vice : : Se r ve r | Sta r ting w w w .example.com on #<Async : : HTTP : : Endpoint http: / / localhost:3000/ {po r t: 3000}> 0.07s info: Async : : Se r vice : : Cont r olle r | Cont r olle r sta r ting . . . 0.6s info: Async : : Containe r : : Notify : : Console | { r eady: t r ue, size: 11} 0.6s info: Async : : Se r vice : : Cont r olle r | Cont r olle r sta r ted . . .

> bundle exec ./falcon. r b 0.0s info: Falcon :

: Command : : Host | Falcon Host v0.52.0 taking flight! | - Conf i gu r ation: ./falcon. r b | - To te r minate: Ct r l-C o r kill 87577 | - To r eload: kill -HUP 87577 0.07s info: Async : : Containe r : : Notify : : Console | {status: "Initializing cont r olle r . . . "} 0.07s info: Falcon : : Se r vice : : Se r ve r | Sta r ting w w w .example.com on #<Async : : HTTP : : Endpoint http: / / localhost:3000/ {po r t: 3000}> 0.07s info: Async : : Se r vice : : Cont r olle r | Cont r olle r sta r ting . . . 0.6s info: Async : : Containe r : : Notify : : Console | { r eady: t r ue, size: 11} 0.6s info: Async : : Se r vice : : Cont r olle r | Cont r olle r sta r ted . . .

Async::Service gem.

# ! /us r /bin/env falcon - host # f

r ozen_st r ing_lite r al: t r ue r equi r e "falcon/envi r onment/ r ack" r equi r e "falcon/envi r onment/lets_enc r ypt_tls" r equi r e "falcon/envi r onment/supe r viso r " se r vice " w w w .example.com" do include Falcon : : Envi r onment : : Rack include Falcon : : Envi r onment : : LetsEnc r yptTLS po r t {ENV.fetch("PORT", 3000).to_i} endpoint {Async : : HTTP : : Endpoint.pa r se("http: / / localhost", po r t: po r t)} end se r vice "backg r ound - jobs" do include Async : : Job : : Adapte r : : ActiveJob : : Envi r onment end

# ! /us r /bin/env falcon - host # f

r ozen_st r ing_lite r al: t r ue r equi r e "falcon/envi r onment/ r ack" r equi r e "falcon/envi r onment/lets_enc r ypt_tls" r equi r e "falcon/envi r onment/supe r viso r " se r vice " w w w .example.com" do include Falcon : : Envi r onment : : Rack include Falcon : : Envi r onment : : LetsEnc r yptTLS po r t {ENV.fetch("PORT", 3000).to_i} endpoint {Async : : HTTP : : Endpoint.pa r se("http: / / localhost", po r t: po r t)} end se r vice "backg r ound - jobs" do include Async : : Job : : Adapte r : : ActiveJob : : Envi r onment end

> pst r ee 88602 -+= 88602 samuel r uby

/Use r s/samuel/.gem/ r uby/3.4.5/bin/falcon - host ./falcon. r b | - - - 88603 samuel w w w .example.com (C=0/0 R=0/0 L=0.0) | - - - 88604 samuel w w w .example.com (C=0/0 R=0/0 L=0.0) | - - - 88605 samuel w w w .example.com (C=0/0 R=0/0 L=0.0) | - - - 88606 samuel w w w .example.com (C=0/0 R=0/0 L=0.0) | - - - 88607 samuel backg r ound - jobs (default R=0 D=0 P=0/0, local) | - - - 88608 samuel backg r ound - jobs (default R=0 D=0 P=0/0, local) | - - - 88609 samuel backg r ound - jobs (default R=0 D=0 P=0/0, local) \ - - - 88610 samuel backg r ound - jobs (default R=0 D=0 P=0/0, local)

> pst r ee 88602 -+= 88602 samuel r uby

falcon.rb de fi nes your deployment. falcon.rb͸σϓϩΠϝϯτΛఆٛ͠·͢ɻ

…including all your services. …͢΂ͯͷαʔϏεΛؚΊͯɻ

…making it easy to deploy anywhere. …Ͳ͜ʹͰ΋؆୯ʹσϓϩΠͰ͖ΔΑ͏ʹ͠·͢ɻ

✅ Hosting

falcon virtual

“Traditional” virtual hosting. ʮैདྷܕʯͷόʔνϟϧϗεςΟϯάɻ

> falcon vi r tual /s r v/http/*/falcon. r b

0.0s info: Falcon : : Command : : Vi r tual | Falcon Vi r tual v0.52.0 taking flight! | - Running on r uby 3.4.5 (2025-07-16 r evision 20cda200d3) +PRISM | - To te r minate: Ct r l-C o r kill 92831 | - To r eload all sites: kill -HUP 92831 . . .

Redirects insecure HTTP to secure HTTPS. ҆શͰͳ͍HTTPΛ҆શͳHTTPS΁ϦμΠϨΫτ͠·͢ɻ

Supports TLS SNI negotiation. TLSͷSNIωΰγΤʔγϣϯΛαϙʔτ͍ͯ͠·͢ɻ

✅ Virtual Hosting

systemd integration. systemdͱͷ౷߹ɻ

# /etc/systemd/system/falcon.se r vice [Unit] Desc r iption=Falcon Vi r

tual Web Se r ve r Afte r =netwo r k.ta r get [Se r vice] Type=notify Envi r onment=VARIANT=p r oduction # Envi r onment=CONSOLE_LEVEL=debug ExecSta r t=/us r /bin/falcon vi r tual "/s r v/http/*/falcon. r b" [Install] WantedBy=multi - use r .ta r get

# /etc/systemd/system/falcon.se r vice [Unit] Desc r iption=Falcon Vi r

✅ systemd Integration

Kubernetes integration. Kubernetesͱͷ౷߹ɻ

containe r s: - name: my - app image: my

- app - image:latest env: - name: NOTIFY_LOG value: "/tmp/notify.log" po r ts: - containe r Po r t: 9292 r eadinessP r obe: exec: command: ["bundle", "exec", "bake", "async:containe r :notify:log: r eady?"] initialDelaySeconds: 5 pe r iodSeconds: 5 failu r eTh r eshold: 12

containe r s: - name: my - app image: my

For liveness probe, application speci fi c is better. Liveness

Probeʹ͸ɺΞϓϦέʔγϣϯݻ༗ͷ΋ͷΛ࢖͏ํ͕๬ ·͍͠Ͱ͢ɻ

For a Rails application, use an HTTP probe. RailsΞϓϦέʔγϣϯͰ͸HTTPϓϩʔϒΛ࢖༻͍ͯͩ͘͠͞ɻ

> cu r l https: / / localhost:3000/up <!DOCTYPE html><html><body

style="backg r ound - colo r : g r een"> < / body> < / html>

livenessP r obe: httpGet: path: /up po r t: 3000

initialDelaySeconds: 10 pe r iodSeconds: 10 failu r eTh r eshold: 3

✅ Kubernetes Integration

Summary Deploying with Falcon ✅ B a sic hosting using

falcon. r b service f iles.

Summary Deploying with Falcon ✅ B a sic hosting using

falcon. r b service f iles. ✅ C a n support multiple services for simpli f ied deployment.

Summary Deploying with Falcon ✅ B a sic hosting using

falcon. r b service f iles. ✅ C a n support multiple services for simpli f ied deployment. ✅ Virtu a l hosting using multiple falcon. r b service f iles.

Summary Deploying with Falcon ✅ B a sic hosting using

falcon. r b service f iles. ✅ C a n support multiple services for simpli f ied deployment. ✅ Virtu a l hosting using multiple falcon. r b service f iles. ✅ Direct support for systemd + NOTIFY_SOCKET.

Summary Deploying with Falcon ✅ B a sic hosting using

falcon. r b service f iles. ✅ C a n support multiple services for simpli f ied deployment. ✅ Virtu a l hosting using multiple falcon. r b service f iles. ✅ Direct support for systemd + NOTIFY_SOCKET. ✅ Decent support for Kubernetes using re a diness probe + NOTIFY_LOG.

3. Monitoring with Falcon

Async::Container

Health Check

If the event loop stalls, it will be detected. Πϕϯτϧʔϓ͕ఀࢭ͢Ε͹ݕग़͞Ε·͢ɻ

Process will be forcefully restarted. ϓϩηε͸ڧ੍తʹ࠶ىಈ͞Ε·͢ɻ

2.01s wa r n: Async : : Containe r :

: Fo r ked | Child failed health check! | { | "child": { | "name": "SleepSe r vice", | "pid": 70187, | “status": null | }, | "age": 2.0107369998004287, | "health_check_timeout": 2 | } 2.02s e r r o r : Async : : Containe r : : Fo r ked | { | "status": "pid 70187 SIGKILL (signal 9)" | }

✅ Health Check

Memory Monitoring

se r vice “ w w w .example.com” do #

. . . othe r conf i gu r ation . . . include Async : : Containe r : : Supe r viso r : : Supe r vised end se r vice "supe r viso r " do include Async : : Containe r : : Supe r viso r : : Envi r onment monito r s do [Async : : Containe r : : Supe r viso r : : Memo r yMonito r .new( # The inte r val at which to check fo r memo r y leaks. inte r val: 1, # The total size limit of all p r ocesses: maximum_size_limit: 1024 * 1024 * 400, # 400 MB )] end end

se r vice “ w w w .example.com” do #

4.07s e r r o r : Async : :

Containe r : : Supe r viso r : : Memo r yMonito r | Memo r y leak detected in p r ocess: | { | "p r ocess_id": 68020, | "monito r ": { | "p r ocess_id": 68020, | "cu r r ent_size": 453509120, | "maximum_size": null, | "maximum_size_limit": 419430400, | "th r eshold_size": 10485760, | "inc r ease_count": 0, | "inc r ease_limit": 20 | } | }

Memory limits are important for application health. ϝϞϦ੍ݶ͸ΞϓϦέʔγϣϯͷ݈શੑʹͱͬͯॏཁͰ͢ɻ

You can create your own monitors. ಠࣗͷϞχλʔΛ࡞੒Ͱ͖·͢ɻ

✅ Memory Monitoring

Traces

Tracing execution is a useful way to monitor performance. ࣮ߦΛτϨʔε͢Δ͜ͱ͸ɺύϑΥʔϚϯεΛ؂ࢹ͢Δ༗ޮͳํ

๏Ͱ͢ɻ

None

Monkey patches everywhere. ࢸΔͱ͜ΖʹϞϯΩʔύον͕͋Γ·͢ɻ

But I wasn’t happy with this. ͔͠͠ɺࢲ͸͜Εʹຬ଍͍ͯ͠·ͤΜͰͨ͠ɻ

So, I created the Traces gem. ͦ͜ͰɺTracesͱ͍͏gemΛ࡞੒͠·ͨ͠ɻ

r equi r e 't r aces' class MyClass def

my_method puts "Hello Wo r ld" end end # If t r acing is disabled, this is a no - op. T r aces : : P r ovide r (MyClass) do def my_method att r ibutes = { 'foo' = > 'ba r ' } T r aces.t r ace('my_method', att r ibutes: att r ibutes) do supe r end end end MyClass.new.my_method

r equi r e 't r aces' class MyClass def

None

Minimal tracing by default. Opt-in model. σϑΥϧτͰ͸࠷খݶͷτϨʔγϯάɻ ΦϓτΠϯϞσϧɻ

> bundle exec bake t r aces:p r ovide r

:list output - - fo r mat json { "async": [ "t r aces/p r ovide r /async/ba r r ie r . r b", "t r aces/p r ovide r /async/task. r b", "t r aces/p r ovide r /async. r b" ], "async - pool": [ "t r aces/p r ovide r /async/pool/cont r olle r . r b" ], "p r otocol - http2": [ "t r aces/p r ovide r /p r otocol/http2/f r ame r . r b", "t r aces/p r ovide r /p r otocol/http2. r b" ] }

# conf i g/t r aces. r b def p

r epa r e # Add HTTP/2 p r otocol t r aces: r equi r e "t r aces/p r ovide r /p r otocol/http2" end

bundle add traces bundle add - - require false \

traces - backend - datadog

TRACES_BACKEND=traces/backend/datadog falcon serve

None

Also, Async::HTTP supports distributed tracing.

bundle add - - require false \ traces - backend

- open_telemetry

✅ Application Tracing

Metrics

Counts, Durations, Sizes Χ΢ϯτɺ࣌ؒɺαΠζ

r equi r e 'met r ics' class MyClass def

self.my_method puts "Hello Wo r ld" end end Met r ics : : P r ovide r (MyClass.singleton_class) do CALL_COUNT = Met r ics.met r ic('call_count', :counte r ) def my_method CALL_COUNT.emit(1) supe r end end MyClass.my_method

r equi r e 'met r ics' class MyClass def

Same deal: mostly opt-in. ಉ༷ʹɺ΄ͱΜͲ͕ΦϓτΠϯͰ͢ɻ

> bundle exec bake met r ics:p r ovide r

:list output - - fo r mat json { "async": [ "met r ics/p r ovide r /async/task. r b", "met r ics/p r ovide r /async. r b" ], "async - http": [ "met r ics/p r ovide r /async/http/client. r b", "met r ics/p r ovide r /async/http/se r ve r . r b", "met r ics/p r ovide r /async/http. r b" ], "async - containe r ": [ "met r ics/p r ovide r /async/containe r /gene r ic. r b", "met r ics/p r ovide r /async/containe r . r b" ] }

# conf i g/met r ics. r b def p

r epa r e # Add HTTP client and se r ve r met r ics: r equi r e "met r ics/p r ovide r /async/http" end

bundle add metrics bundle add - - require false \

metrics - backend - datadog

METRICS_BACKEND=metrics/backend/datadog falcon serve

None

Pro fi ler Traces Metrics

Pro fi ler Traces Metrics More Det a il Less

Det a il

Pro fi ler Traces Metrics Did something go wrong? Wh

a t f a iled? How did it f a il? More Det a il Less Det a il

Bigger Overhe a d More D a t a Sm

a ller Overhe a d Less D a t a Pro fi ler Traces Metrics Did something go wrong? Wh a t f a iled? How did it f a il? More Det a il Less Det a il

✅ Application Metrics

Logging

The Console gem provides a simple logging interface. Console gem͸γϯϓϧͳϩάΠϯλʔϑΣʔεΛఏڙ͠·͢ɻ

Console.info(self, "Hello Wo r ld", st r uctu r ed:

"data") Subject Mess a ge Structured D a t a

r equi r e "console" Console.info(self, "Hello Wo r ld",

st r uctu r ed: "data") Console.debug(self, "Debugging info r mation", session: r equest.session) Console.wa r n(self, "This is a wa r ning") Console.e r r o r (self, "An e r r o r occu r r ed", exception: e r r o r ) Console.fatal(self, "A fatal e r r o r occu r r ed", exception: e r r o r )

It is possible to enrich logs with extra information. ϩάʹ௥Ճ৘ใΛ෇Ճ͢Δ͜ͱ͕ՄೳͰ͢ɻ

# conf i g/console. r b def make_output(io = nil,

env = ENV, * * options) r equi r e "console/output/datadog" Console : : Output : : Datadog.new(supe r ) r escue LoadE r r o r supe r end

None

Adapters support existing libraries. Ξμϓλ͸طଘͷϥΠϒϥϦΛαϙʔτ͍ͯ͠·͢ɻ

bundle add \ console - adapter - rails

23.18s info: p r ocess_action.action_cont r olle r : Incoming

r equest: GET "/". | { | "cont r olle r ": "WelcomeCont r olle r ", | "action": "index", | "fo r mat": "html", | "method": "GET", | "path": "/", | "status": 200, | "view_ r untime": 33.49500012397766, | "db_ r untime": 0.0, | "que r ies_count": 0, | "cached_que r ies_count": 0, | "sou r ce_add r ess": " : : 1", | "allocations": 60143, | "du r ation": 36.60800004005432 | }

✅ Logging

Summary Monitoring with Falcon ✅ Autom a tic he a

lth checks detect h a ngs a nd st a lls.

Summary Monitoring with Falcon ✅ Autom a tic he a

lth checks detect h a ngs a nd st a lls. ✅ Supervisor fr a mework c a n monitor memory us a ge + custom monitors.

Summary Monitoring with Falcon ✅ Autom a tic he a

lth checks detect h a ngs a nd st a lls. ✅ Supervisor fr a mework c a n monitor memory us a ge + custom monitors. ✅ Flexible a pplic a tion tr a cing + distributed tr a cing.

Summary Monitoring with Falcon ✅ Autom a tic he a

lth checks detect h a ngs a nd st a lls. ✅ Supervisor fr a mework c a n monitor memory us a ge + custom monitors. ✅ Flexible a pplic a tion tr a cing + distributed tr a cing. ✅ Flexible a pplic a tion metrics.

Summary Monitoring with Falcon ✅ Autom a tic he a

lth checks detect h a ngs a nd st a lls. ✅ Supervisor fr a mework c a n monitor memory us a ge + custom monitors. ✅ Flexible a pplic a tion tr a cing + distributed tr a cing. ✅ Flexible a pplic a tion metrics. ✅ Logging with tr a ce correl a tion a nd f lexible processing.

Building, Deploying, and Monitoring Ruby Web Ap...

Building, Deploying, and Monitoring Ruby Web Applications with Falcon (Kaigi on Rails 2025)

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