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Hey! You're still here?

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Great! I have a bonus chapter for you.

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One of our interns, Hugo, is complaining
that he has to log in to our server

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and run the booking reminders
command, every night at midnight.

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I don't know what the problem is -
isn't that what interns are for?!

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But... I guess to be more robust, we should
automate this in case he's sick or forgets.

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We could set up a CRON job...

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but that wouldn't be nearly as cool or flexible
as using the Symfony Scheduler component.

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It's perfect for this.

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At your terminal, run: composer
require scheduler Think

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of Symfony Scheduler as an add-on for Messenger.

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It provides its own special
transport that, instead of a queue,

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determines if it's time to run a job.

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Each job, or task, is a messenger
message, so it requires a message handler.

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You consume the schedule, like any messenger
transport with the messenger:consume command.

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Create a schedule with: symfony
console make:schedule Transport name?

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Use default.

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Schedule name?

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Use the default: MainSchedule.

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Exciting! It's possible to
have multiple schedules,

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but for most apps, a single schedule is enough.

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Check it out: src/Scheduler/MainSchedule.php.

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It's a service that implements
ScheduleProviderInterface and is marked

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with the #[AsSchedule] attribute
with the name default.

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The maker automatically injected the
cache, and we'll see why in a second.

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The getSchedule() method is where we
configure the schedule and add tasks.

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This ->stateful() that we're passing
$this->cache to is important.

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If the process that's running
this schedule goes down -

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like our messenger workers stop
temporarily during a server restart -

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when it comes back online, it will know
all the jobs it missed and run them.

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If a task was supposed to run 10 times
while it was down, it will run them all.

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That might not be desired so add
->processOnlyLastMissedRun(true)

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to only run the last one: Bulletproof!

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For more complex apps, you might be consuming
the same schedule on multiple workers.

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Use ->lock() to configure a lock so that
only one worker runs the task when its due.

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Time to add our first task!

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In ->add(), write RecurringMessage::.

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There are a few different
ways to trigger a task.

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I like to use cron().

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I want this task to run at midnight, every day,

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so use 0 0 * * *. The second argument
is the messenger message to dispatch.

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We want to run the SendBookingRemindersCommand,
but we can't add it here directly.

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Instead, use new RunCommandMessage()
and pass the command name:

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app:send-booking-reminders (you can
pass arguments and options here too):

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At your terminal, list our
schedule's tasks by running:

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symfony console debug:schedule
Oh, we have an error.

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You cannot use "CronExpressionTrigger" as the

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"cron expression" package is not installed
Easy fix: copy the install command and run it:

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composer require dragonmantank/cron-expression
Cool name!

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Now run the debug command again: Here we go, the
output's a little wonky on this small screen,

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but you can see the cron
expression, the message (and command),

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and the next runtime: tonight at midnight.

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There's an alternate to schedule commands.

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In MainSchedule::getSchedule(),
delete the ->add().

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Then jump over to our
SendBookingRemindersCommand

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and add another attribute: #[AsCronTask()]
passing: 0 0 * * *: In your terminal,

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debug the schedule again to make sure
it's still listed: And it is, pretty neat.

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If you have a lot of tasks scheduled
at the same time, like midnight,

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you might see a CPU spike
at this time on your server.

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Unless it's super important that tasks run at a
very specific time, you should spread them out.

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One way to do this of course, is to manually
make sure they all have different cron

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expressions but...

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that's a bore.

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For our app:send-booking-reminders command,

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I don't care when it runs,
just that it runs once a day.

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We can use a hashed cron expression.

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In our expression, replace the 0's with #'s.

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The # means "pick a random,
valid value for this part":

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Debug the schedule again:
It's set to run at 5:11am.

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Run the command again: It's still 5:11am.

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Ok, so it's not truly random, the values
are calculated deterministically based

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on the message details.

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In our case, the string
app:send-booking-reminders.

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A different command with the same hash
expression will have different values.

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The Scheduler documentation
has all the details on this.

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There's even aliases for common hashes.

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For instance, #mignight will pick
a time between midnight and 3am.

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Use that for our expression: and debug the
schedule again: Oops, a typo, I'll fix that

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and run again: It's now scheduled
to run every day at 2:11am.

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Cool! We've configured our
schedule, but how do we run it?

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Remember, schedules are just
Messenger transports.

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The transport name is scheduler_<schedule_name>,
in our case, scheduler_default.

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Run it with: symfony console messenger:consume
scheduler_default On your production server,

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configure this to run in the background
just like a normal messenger worker.

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Alright, that's a quick rundown
of the Scheduler component.

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Check out the documentation
to learn more about it!

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Happy coding and happy scheduling!