Kiq v0.3.0 Kiq behaviour View Source
Kiq is a robust and extensible job processing queue that aims for compatibility with Sidekiq Enterprise.
Job queuing, processing and reporting are all built on GenStage. That means maximum parallelism with the safety of backpressure as jobs are processed.
Usage
Kiq isn’t an application that must be started. Similarly to Ecto, you define one or more Kiq modules within your application. This allows multiple supervision trees with entirely different configurations.
Define a Kiq module for your application:
defmodule MyApp.Kiq do
use Kiq, queues: [default: 25, events: 50]
end
Include the module in your application’s supervision tree:
defmodule MyApp.Application do
@moduledoc false
use Application
alias MyApp.{Endpoint, Kiq, Repo}
def start(_type, _args) do
children = [
{Repo, []},
{Endpoint, []},
{Kiq, []}
]
Supervisor.start_link(children, strategy: :one_for_one, name: MyApp.Supervisor)
end
end
Configuration
Kiq is used to start one or more supervision trees in your application. That means there isn’t a central Kiq “app” to configure, instead each supervision tree may be configured independently.
Configuration options pass through a couple of locations, accumulating
overrides until finally passing through the init/2
callback. Options are
accumulated in this order:
- Options passed into via the
use
macro. These should be constant compile time options, i.e.extra_reporters
. - Options passed to
start_link/1
by the application’s supervision tree. These should also be values suitable for compile time. - Injected by the
init/2
callback inside your application’s Kiq instance. This is where runtime configuration such as the Redis URL or environment specific options should be passed. The options can come from any dynamic source such as Mix Config, Vault, Etcd, environment variables, etc.
The default init/2
implementation uses System.get_env/1
to read the
REDIS_URL
on boot. The default callback can be overridden to pull in
additional configuration. For example, to grab values from
Application.get_env/2
:
@impl Kiq
def init(_reason, opts) do
for_env = Application.get_env(:my_app, :kiq, [])
opts =
opts
|> Keyword.merge(for_env)
|> Keyword.put(:client_opts, [redis_url: System.get_env("REDIS_URL")])
{:ok, opts}
end
The opts
argument contains all configuration from stages 1 and 2 (the use
macro and the call to start_link/1
).
Configuration Options
client_opts
— A keyword list of options passed to each Redix connection. If the opts contain the keyredis_url
then it will be passed toRedix.start_link/1
as the lone argument.extra_reporters
— Additional reporters that your application will use to report errors, track external stats, etc.fetch_interval
— How frequently to poll for new jobs. Polling only happens when consumers aren’t actively requesting new jobs.flush_interval
- How frequently locally enqueued jobs will be pushed to Redis. This defaults to10ms
, though it will back-off by a factor of1.5
if there are any connection errors.pool_size
— Controls the number of Redis connections available to Kiq, defaults to 5.queues
— A keyword list of queues where each entry is the name of the queue and the concurrency setting. For example, setting[default: 10, exports: 5, media: 5]
would start the queuesdefault
,exports
andmedia
with a combined concurrency of 20. The concurrency setting specifies how many jobs each queue will run concurrently.schedulers
— A list of schedulers to run. The default schedulers are “retry” which is used to retry failed jobs with a backoff and “schedule”, used to enqueue jobs at a specific time in the future. Set this to an empty list to disable all schedulers and allow Sidekiq to handle enqueuing retries and scheduled jobs.server?
— Whether to start the queue supervisors and start processing jobs or only start the client. This setting is useful for testing or deploying your application’s web and workers separately.test_mode
— Either:disabled
or:sandbox
. See Testing for details.
Testing
Kiq has special considerations to facilitate isolated and asynchronous testing.
For testing Kiq should be configured in :sandbox
mode and have the server
disabled. This can be done specifically for the test environment by adding
config to config/test.exs
:
config :my_app, :kiq, server?: false, test_mode: :sandbox
Running in :sandbox
mode ensures that enqueued jobs stay in memory and are
never flushed to Redis. This allows your tests to use Kiq.Testing
to make
quick assertions about which jobs have or haven’t been enqueued. See the docs
for Kiq.Testing
for more details and usage.
Reliable Push
Reliable push replicates the safety aspects of Sidekiq Pro’s reliability client. To guard against network errors or other Redis issues the client buffers all jobs locally. At a frequent interval the jobs are flushed to Redis. If there are any errors while flushing the jobs will remain in memory until flushing can be retried later.
Caveats
- The local job buffer is stored in memory, if the server is restarted suddently some jobs may be lost.
- There isn’t any limit on the number of jobs that can be buffered. However, to conserve space jobs are stored compressed.
Private Queues
Kiq tries to prevent all job loss through private queues, a variant of the Super Fetch mechanism available in Sidekiq Pro. When jobs are executed they are backed up to a private queue specific to the server processing the job. If the processor crashes or the application is terminated before the job is finished the jobs remain backed up. On startup, and periodically afterward, jobs in any dead private queues are pushed back to the public queue for re-execution.
This solution is well suited to containerized environments and autoscaling.
Unique Jobs
Kiq supports Sidekiq Enterprise’s unique jobs. This feature prevents enqueueing duplicate jobs while an original job is still pending. The operations that attempt to enforce uniqueness are not atomic—uniquess is not guaranteed and should be considered best effort.
Enable unique jobs for a worker by setting a unique time period:
use Kiq.Worker, unique_for: :timer.minutes(5)
Unlock Policy
By default unique jobs will hold the unique lock until the job has ran successfully. This policy ensures that jobs will remain locked if there are any errors, but it is prone to race conditions in certain situations for longer running jobs.
Generally it is best to stick with the default :success
policy. However, if
your job is effected by the race condition you can change your worker’s
policy:
use Kiq.Worker, unique_for: :timer.minutes(60), unique_until: :start
Caveats
- Note that job uniqueness is calculated from the
class
,args
, andqueue
. This means that jobs with identical args may be added to different queues. - Unique jobs enqueued by Sidekiq will be unlocked by Kiq, but they may not use the same lock value. This is due to differences between hashing Erlang terms and Ruby objects. To help ensure uniqueness always enqueue unique jobs from either Sidekiq or Kiq.
Expiring Jobs
Kiq supports Sidekiq Pro’s expiring jobs. Expiring jobs won’t be ran
after a configurable amount of time. The expiration period is set with the
expires_in
option, which accepts millisecond values identically
unique_for
.
Set the expiration for a worker using a relative time:
use Kiq.Worker, expires_in: :timer.hours(1)
Expiration time applies after the scheduled time. That means scheduling a job to run in an hour, with an expiration of 30 minutes, will expire in one hour and 30 minutes.
Link to this section Summary
Callbacks
Clear all enqueued, scheduled and backup jobs
Enqueue a job to be processed asynchronously
A callback executed when the supervision tree is started and possibly when configuration is read
Starts the client and possibly the supervision tree, returning {:ok, pid}
when startup is
successful
Link to this section Types
Link to this section Callbacks
Clear all enqueued, scheduled and backup jobs.
All known queues are cleared, even if they aren’t listed in the current configuration.
enqueue(job_args(), job_opts()) :: {:ok, Kiq.Job.t()} | {:error, Exception.t()}
Enqueue a job to be processed asynchronously.
Jobs can be enqueued from Job
structs, maps or keyword lists.
Options
in
- The amount of time in seconds to wait before processing the job. This must be a positive integer.at
- A specificDateTime
in the future when the job should be processed.
Examples
# Enqueue a job to be processed immediately
MyJob.new([1, 2]) |> MyKiq.enqueue()
# Enqueue a job in one minute
MyJob.new([1, 2]) |> MyKiq.enqueue(in: 60)
# Enqueue a job some time in the future
MyJob.new([1, 2]) |> MyKiq.enqueue(at: ~D[2020-09-20 12:00:00])
# Enqueue a job from scratch, without using a worker module
MyKiq.enqueue(class: "ExternalWorker", args: [1])
A callback executed when the supervision tree is started and possibly when configuration is read.
The first argument is the context of the callback being invoked. In most circumstances this
will be :supervisor
. The second argument is a keyword list of the combined options passed
to use/1
and start_link/1
.
Application configuration is not passed into the init/2
callback. To use application
config the callback must be overridden and merged manually.
start_link(opts :: Keyword.t()) :: Supervisor.on_start()
Starts the client and possibly the supervision tree, returning {:ok, pid}
when startup is
successful.
Returns {:error, {:already_started, pid}}
if the tree is already started or {:error, term}
in case anything else goes wrong.
Options
Any options passed to start_link
will be merged with those provided in the use
block.