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request_throttle.rb
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request_throttle.rb
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# frozen_string_literal: true
#
# Copyright (C) 2013 - present Instructure, Inc.
#
# This file is part of Canvas.
#
# Canvas is free software: you can redistribute it and/or modify it under
# the terms of the GNU Affero General Public License as published by the Free
# Software Foundation, version 3 of the License.
#
# Canvas is distributed in the hope that it will be useful, but WITHOUT ANY
# WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
# A PARTICULAR PURPOSE. See the GNU Affero General Public License for more
# details.
#
# You should have received a copy of the GNU Affero General Public License along
# with this program. If not, see <http://www.gnu.org/licenses/>.
#
class RequestThrottle
attr_accessor :inst_access_token_authentication
# this @@last_sample data isn't thread-safe, and if canvas ever becomes
# multi-threaded, we'll have to just get rid of it since we can't measure
# per-thread heap used
@@last_sample = 0
SERVICE_HEADER_EXPRESSION = %r{^inst-[a-z0-9_-]+/[a-z0-9]+.*$}i
class ActionControllerLogSubscriber < ActiveSupport::LogSubscriber
def process_action(event)
# we don't have access to the request here, so we can't just put this in the env
Thread.current[:request_throttle_db_runtime] = (event.payload[:db_runtime] || 0) / 1000.0
end
end
ActionControllerLogSubscriber.attach_to :action_controller
def db_runtime(_request)
Thread.current[:request_throttle_db_runtime]
end
def initialize(app)
@app = app
@inst_access_token_authentication = nil
end
def call(env)
starting_mem = Canvas.sample_memory
starting_cpu = Process.times
request = ActionDispatch::Request.new(env)
self.inst_access_token_authentication = ::AuthenticationMethods::InstAccessToken::Authentication.new(
request
)
# NOTE: calling fullpath was a workaround for a rails bug where some ActionDispatch::Request methods blow
# up when using certain servers until fullpath is called once to set env['REQUEST_URI']
# so don't remove
path = request.fullpath
status, headers, response = nil
throttled = false
bucket = LeakyBucket.new(client_identifier(request))
up_front_cost = bucket.get_up_front_cost_for_path(path)
pre_judged = approved?(request) || blocked?(request)
cost = bucket.reserve_capacity(up_front_cost, request_prejudged: pre_judged) do
status, headers, response = if allowed?(request, bucket)
@app.call(env)
else
throttled = true
rate_limit_exceeded
end
ending_cpu = Process.times
ending_mem = Canvas.sample_memory
user_cpu = ending_cpu.utime - starting_cpu.utime
system_cpu = ending_cpu.stime - starting_cpu.stime
account = env["canvas.domain_root_account"]
db_runtime = self.db_runtime(request) || 0.0
report_on_stats(db_runtime, account, starting_mem, ending_mem, user_cpu, system_cpu)
cost = calculate_cost(user_cpu, db_runtime, env)
cost
end
if client_identifier(request) && !client_identifier(request).starts_with?("session")
headers["X-Request-Cost"] = cost.to_s unless throttled
headers["X-Rate-Limit-Remaining"] = bucket.remaining.to_s
headers["X-Rate-Limit-Remaining"] = 0.0.to_s if blocked?(request)
end
[status, headers, response]
end
# currently we define cost as the amount of user cpu time plus the amount
# of time spent in db queries, plus any arbitrary cost the app assigns.
# The CPU and DB costs are weighted according to settings so they
# can be dialed up or down individually if we need to have them contribute more or
# less to overall throttling behaviour. Overall throttling prevelency
# not related to any specific subcategory of time sinks should be controlled by tuning the
# "request_throttle.outflow" setting instead, which impacts how quickly
# the bucket leaks.
def calculate_cost(user_time, db_time, env)
extra_time = env.fetch("extra-request-cost", 0)
extra_time = 0 unless extra_time.is_a?(Numeric) && extra_time >= 0
cpu_cost = Setting.get("request_throttle.cpu_cost_weight", "1.0").to_f
db_cost = Setting.get("request_throttle.db_cost_weight", "1.0").to_f
(user_time * cpu_cost) + (db_time * db_cost) + extra_time
end
def subject_to_throttling?(request)
self.class.enabled? && Canvas.redis_enabled? && !approved?(request) && !blocked?(request)
end
def allowed?(request, bucket)
if approved?(request)
true
elsif blocked?(request)
# blocking is useful even if throttling is disabled, this is left in intentionally
Rails.logger.info("blocking request due to blocklist, client id: #{client_identifiers(request).inspect} ip: #{request.remote_ip}")
InstStatsd::Statsd.increment("request_throttling.blocked")
false
else
if bucket.full?
if RequestThrottle.enabled?
InstStatsd::Statsd.increment("request_throttling.throttled")
Rails.logger.info("blocking request due to throttling, client id: #{client_identifier(request)} bucket: #{bucket.to_json}")
return false
else
Rails.logger.info("WOULD HAVE throttled request (config disabled), client id: #{client_identifier(request)} bucket: #{bucket.to_json}")
end
end
true
end
end
def blocked?(request)
return true if inst_access_token_authentication&.blocked?
client_identifiers(request).any? { |id| self.class.blocklist.include?(id) }
end
def approved?(request)
client_identifiers(request).any? { |id| self.class.approvelist.include?(id) }
end
def client_identifier(request)
client_identifiers(request).first
end
def tag_identifier(tag, identifier)
return unless identifier
"#{tag}:#{identifier}"
end
# This is cached on the request, so a theoretical change to the request
# object won't be caught.
def client_identifiers(request)
request.env["canvas.request_throttle.user_id"] ||= [
tag_identifier("lti_advantage", lti_advantage_client_id_and_cluster(request)),
tag_identifier("service_user_key", site_admin_service_user_key(request)),
tag_identifier("service_user_key", inst_access_token_authentication&.tag_identifier),
(token_string = AuthenticationMethods.access_token(request, :GET).presence) && "token:#{AccessToken.hashed_token(token_string)}",
tag_identifier("user", AuthenticationMethods.user_id(request).presence),
tag_identifier("session", session_id(request).presence),
tag_identifier("tool", tool_id(request)),
tag_identifier("ip", request.ip)
].compact
end
# Bucket based on LTI Advantage client_id. Routes are identified by a combination of path
# and whether the controller uses the LtiServices concern -- see lti_advantage_route? method.
def lti_advantage_client_id_and_cluster(request)
return unless Lti::IMS::AdvantageAccessTokenRequestHelper.lti_advantage_route?(request)
client_id = Lti::IMS::AdvantageAccessTokenRequestHelper.token(request)&.client_id
return unless client_id
cluster_id = request.env["canvas.domain_root_account"]&.shard&.database_server_id
"#{client_id}-#{cluster_id}"
rescue Lti::IMS::AdvantageErrors::AdvantageClientError
nil
end
def tool_id(request)
return unless request.request_method_symbol == :post && request.fullpath =~ %r{/api/lti/v1/tools/([^/]+)/(?:ext_)?grade_passback}
tool_id = $1
return unless Api::ID_REGEX.match?(tool_id)
# yes, a db lookup, but we're only loading it for these two actions,
# and only if another identifier couldn't be found
tool = ContextExternalTool.find_by(id: tool_id)
return unless tool
tool.domain
end
def session_id(request)
request.env["rack.session.options"].try(:[], :id)
end
def site_admin_service_user_key(request)
# We only want to allow this approvelist method for User-Agent strings that match the following format:
# Example (short): `inst-service-name/2d0c1jk2`
# Example (full): `inst-service-name/2d0c1jk2 (region: us-east-1; host: 1de983c20j1ak2; env: production)`
return unless SERVICE_HEADER_EXPRESSION.match?(request.user_agent)
return unless (token_string = AuthenticationMethods.access_token(request))
return unless AccessToken.site_admin?(token_string)
AccessToken.authenticate(token_string).global_developer_key_id
end
def service_user_jwt_key(request)
AuthenticationMethods::InstAccessToken.tag_identifier(request)
end
def self.blocklist
@blocklist ||= list_from_setting("request_throttle.blocklist")
end
def self.approvelist
@approvelist ||= list_from_setting("request_throttle.approvelist")
end
def self.reload!
@approvelist = @blocklist = @dynamic_settings = nil
LeakyBucket.reload!
end
def self.enabled?
Setting.get("request_throttle.enabled", "true") == "true"
end
def self.list_from_setting(key)
Set.new(Setting.get(key, "").split(",").map { |i| i.gsub(/^\s+|\s*(?:;.+)?\s*$/, "") }.compact_blank)
end
def self.dynamic_settings
unless @dynamic_settings
consul_data = DynamicSettings.find(tree: :private)["request_throttle.yml", failsafe: :missing] || ""
return {} if consul_data == :missing
@dynamic_settings = YAML.safe_load(consul_data) || {}
end
@dynamic_settings
end
def rate_limit_exceeded
[403,
{ "Content-Type" => "text/plain; charset=utf-8", "X-Rate-Limit-Remaining" => "0.0" },
["403 #{Rack::Utils::HTTP_STATUS_CODES[403]} (Rate Limit Exceeded)\n"]]
end
def report_on_stats(db_runtime, account, starting_mem, ending_mem, user_cpu, system_cpu)
RequestContext::Generator.add_meta_header("b", starting_mem)
RequestContext::Generator.add_meta_header("m", ending_mem)
RequestContext::Generator.add_meta_header("u", "%.2f" % [user_cpu])
RequestContext::Generator.add_meta_header("y", "%.2f" % [system_cpu])
RequestContext::Generator.add_meta_header("d", "%.2f" % [db_runtime])
if account&.shard&.database_server
InstStatsd::Statsd.timing("requests_system_cpu.cluster_#{account.shard.database_server.id}",
system_cpu,
short_stat: "requests_system_cpu",
tags: { cluster: account.shard.database_server.id })
InstStatsd::Statsd.timing("requests_user_cpu.cluster_#{account.shard.database_server.id}",
user_cpu,
short_stat: "requests_user_cpu",
tags: { cluster: account.shard.database_server.id })
end
mem_stat = if starting_mem == 0 || ending_mem == 0
"? ? ? ?"
else
"#{starting_mem} #{ending_mem} #{ending_mem - starting_mem} #{@@last_sample}"
end
Rails.logger.info "[STAT] #{mem_stat} #{user_cpu} #{system_cpu}"
@@last_sample = ending_mem
end
# Our leaky bucket has a separate high water mark (where the bucket is
# considered "full") and maximum.
# Think of the HWM as a line on the inside of the bucket, where the bucket is
# considered full if the bucket gets filled past that line, but the bucket
# can continue to hold more up to the maximum (top of the bucket).
# The reason we add this to the normal leaky bucket algorithm is if maximum
# and hwm were equal, then the bucket would always leak at least a tiny bit
# by the beginning of the next request, and thus would never be considered
# full.
LeakyBucket = Struct.new(:client_identifier, :count, :last_touched) do # rubocop:disable Lint/StructNewOverride
def initialize(client_identifier, count = 0.0, last_touched = nil)
super
end
def redis
@redis ||= Canvas.redis.respond_to?(:node_for) ? Canvas.redis.node_for(cache_key) : Canvas.redis
end
# Cache this on the class, so we don't load the lua script on each request.
def self.lua
@lua ||= ::Redis::Scripting::Module.new(nil, File.join(File.dirname(__FILE__), "request_throttle"))
end
def cache_key
"request_throttling:#{client_identifier}"
end
{
maximum: 800,
hwm: 600,
outflow: 10,
up_front_cost: 50,
}.each do |(setting, default)|
define_method(setting) do
(self.class.custom_settings_hash[client_identifier]&.[](setting.to_s) ||
Setting.get("request_throttle.#{setting}", default)).to_f
end
end
def self.custom_settings_hash
@custom_settings_hash ||= begin
JSON.parse(
Setting.get("request_throttle.custom_settings", "{}")
)
rescue JSON::JSONError
{}
end
end
def self.up_front_cost_by_path_regex
@up_front_cost_regex_map ||=
begin
hash = RequestThrottle.dynamic_settings["up_front_cost_by_path_regex"] || {}
hash.keys.select { |k| k.is_a?(String) }.map { |k| hash[Regexp.new(k)] = hash.delete(k) } # regexify strings
hash.each do |k, v|
next if k.is_a?(Regexp) && v.is_a?(Numeric)
::Rails.logger.error("ERROR in request_throttle.yml: up_front_cost_by_path_regex must use Regex => Numeric key-value pairs")
hash.clear
break
end
hash
end
end
def self.reload!
@custom_settings_hash = nil
@up_front_cost_regex_map = nil
end
# up_front_cost is a placeholder cost. Essentially it adds some cost to
# doing multiple requests in parallel, but that cost is transient -- it
# disappears again when the request finishes.
def get_up_front_cost_for_path(path)
# if it matches any of the regexes in the setting, return the specified cost
self.class.up_front_cost_by_path_regex.each do |regex, cost|
return cost if regex&.match?(path)
end
up_front_cost # otherwise use the default
end
# This method does an initial increment by the up_front_cost, loading the
# data out of redis at the same time. It then yields to the block,
# expecting the block to return the final cost. It then increments again,
# subtracting the initial up_front_cost from the final cost to erase it.
def reserve_capacity(up_front_cost = self.up_front_cost, request_prejudged: false)
increment(0, up_front_cost) unless request_prejudged
cost = yield
ensure
increment(cost || 0, -up_front_cost) unless request_prejudged
end
def full?
count >= hwm
end
def remaining
hwm - count
end
# This is where we both leak and then increment by the given cost amount,
# all in lua on the redis server.
# We do this all in lua to save on redis calls.
# Without lua, we'd have to use a redis optimistic transaction, reading the
# old values, and then pushing the new values. That would take at least 2
# round trips, and possibly more when we get a transaction conflict.
# amount and reserve_cost are passed separately for logging purposes.
def increment(amount, reserve_cost = 0, current_time = Time.now)
if client_identifier.blank? || !Canvas.redis_enabled?
return
end
current_time = current_time.to_f
Rails.logger.debug("request throttling increment: #{([amount, reserve_cost, current_time] + as_json.to_a).to_json}")
count, last_touched = LeakyBucket.lua.run(:increment_bucket, [cache_key], [amount + reserve_cost, current_time, outflow, maximum], redis)
self.count = count.to_f
self.last_touched = last_touched.to_f
rescue Redis::BaseConnectionError
# ignore
end
end
end
Canvas::Reloader.on_reload { RequestThrottle.reload! }