Grant Street Group
and 1 contributors

NAME

HealthCheck - A health check for your code

VERSION

version v1.5.4

SYNOPSIS

    use HealthCheck;

    # a check can return a hashref containing anything at all,
    # however some values are special.
    # See the HealthCheck Standard for details.
    sub my_check {
        return {
            anything => "at all",
            id       => "my_check",
            status   => 'WARNING',
        };
    }

    my $checker = HealthCheck->new(
        id     => 'main_checker',
        label  => 'Main Health Check',
        tags   => [qw( fast cheap )],
        checks => [
            sub { return { id => 'coderef', status => 'OK' } },
            'my_check',          # Name of a method on caller
        ],
    );

    my $other_checker = HealthCheck->new(
        id     => 'my_health_check',
        label  => "My Health Check",
        tags   => [qw( cheap easy )],
        other  => "Other details to pass to the check call",
    )->register(
        'My::Checker',       # Name of a loaded class that ->can("check")
        My::Checker->new,    # Object that ->can("check")
    );

    # It's possible to add ids, labels, and tags to your checks
    # and they will be copied to the Result
    $other_checker->register( My::Checker->new(
        id    => 'my_checker',
        label => 'My Checker',
        tags  => [qw( cheap copied_to_the_result )]
    ) );

    # You can add HealthCheck instances as checks
    # You could add a check to itself to create an infinite loop of checks.
    $checker->register( $other_checker );

    # A hashref of the check config
    # This whole hashref is passed as an argument
    # to My::Checker->another_check
    $checker->register( {
        invocant    => 'My::Checker',      # to call the "check" on
        check       => 'another_check',    # name of the check method
        tags        => [qw( fast easy )],
        more_params => 'anything',
    } );

    my @tags = $checker->tags;    # returns fast, cheap

    my %result = %{ $checker->check( tags => ['cheap'] ) };
       # OR run the opposite checks
       %result = %{ $checker->check( tags => ['!cheap'] ) };

    # A checker class or object just needs to have either
    # a check method, which is used by default,
    # or another method as specified in a hash config.
    package My::Checker;

    # Optionally subclass HealthCheck::Diagnostic
    use parent 'HealthCheck::Diagnostic';

    # and provide a 'run' method, the Diagnostic base class will
    # pass your results through the 'summarize' helper that
    # will add warnings about invalid values as well as
    # summarizing multiple results.
    sub run {
        return {
            id     => ( ref $_[0] ? "object_method" : "class_method" ),
            status => "WARNING",
        };
    }

    # Any checks *must* return a valid "Health Check Result" hashref.

    # You can add your own check that doesn't call 'summarize'
    # or, overload the 'check' helper in the parent class.
    sub another_check {
        my ($self, %params) = @_;
        return {
            id     => 'another_check',
            label  => 'A Super custom check',
            status => ( $params{more_params} eq 'fine' ? "OK" : "CRITICAL" ),
        };
    }

%result will be from the subset of checks run due to the tags.

    $checker->check(tags => ['cheap']);

    id      => "main_checker",
    label   => "Main Health Check",
    tags    => [ "fast", "cheap" ],
    status  => "WARNING",
    results => [
        {   id     => "coderef",
            status => "OK",
            tags   => [ "fast", "cheap" ]  # inherited
        },
        {   anything => "at all",
            id       => "my_check",
            status   => "WARNING",
            tags     => [ "fast", "cheap" ] # inherited
        },
        {   id      => "my_health_check",
            label   => "My Health Check",
            tags    => [ "cheap", "easy" ],
            status  => "WARNING",
            results => [
                {   id     => "class_method",
                    tags   => [ "cheap", "easy" ],
                    status => "WARNING",
                },
                {   id     => "object_method",
                    tags   => [ "cheap", "easy" ],
                    status => "WARNING",
                },
                {   id     => "object_method",
                    label  => "My Checker",
                    tags   => [ "cheap", "copied_to_the_result" ],
                    status => "WARNING",
                }
            ],
        }
    ],

DESCRIPTION

Allows you to create callbacks that check the health of your application and return a status result.

There are several things this is trying to enable:

  • A fast HTTP endpoint that can be used to verify that a web app can serve traffic.

  • A more complete check that verifies all the things work after a deployment.

  • The ability for a script, such as a cronjob, to verify that it's dependencies are available before starting work.

  • Different sorts of monitoring checks that are defined in your codebase.

Results returned by these checks should correspond to the GSG Health Check Standard.

You may want to use HealthCheck::Diagnostic to simplify writing your check slightly.

METHODS

new

    my $checker = HealthCheck->new( id => 'my_checker' );

ATTRIBUTES

checks

An arrayref that is passed to "register" to initialize checks.

tags

An arrayref used as the default set of tags for any checks that don't override them.

Any other parameters are included in the "Result" hashref returned.

Some recommended things to include are:

id

The unique id for this check.

label

A human readable name for this check.

register

    $checker->register({
        invocant => $class_or_object,
        check    => $method_on_invocant_or_coderef,
        more     => "any other params are passed to the check",
    });

Takes a list or arrayref of check definitions to be added to the object.

Each registered check must return a valid GSG Health Check response, either as a hashref or an even-sized list. See the GSG Health Check Standard (linked in "DESCRIPTION") for the fields that checks should return.

Rather than having to always pass in the full hashref definition, several common cases are detected and used to fill out the check.

coderef

If passed a coderef, this will be called as the check without an invocant.

object

If a blessed object is passed in and it has a check method, use that for the check, otherwise throw an exception.

string

If a string is passed in, check if it is the name of a loaded class that has a check method, and if so use it as the invocant with the method as the check. Otherwise if our caller has a method with this name, the caller becomes the invocant and this becomes the check, otherwise throws an exception.

full hashref of params

The full hashref can consist of a check key that the above heuristics are applied, or include an invocant key that is used as either an object or class name. With the invocant specified, the now optional check key defaults to "check" and is used as the method to call on invocant.

All attributes other than invocant and check are passed to the check.

check

    my %results = %{ $checker->check(%params) }

Calls all of the registered checks and returns a hashref of the results of processing the checks passed through "summarize". Passes the "full hashref of params" as an even-sized list to the check, without the invocant or check keys. This hashref is shallow merged with and duplicate keys overridden by the %params passed in.

If there is both an invocant and check in the params, it the check is called as a method on the invocant, otherwise check is used as a callback coderef.

If only a single check is registered, the results from that check are merged with, and will override the "ATTRIBUTES" set on the object instead of being put in a results arrayref.

Throws an exception if no checks have been registered.

run

Main implementation of the checker is here.

INTERNALS

These methods may be useful for subclassing, but are not intended for general use.

should_run

    my $bool = $checker->should_run( \%check, tags => ['apple', '!banana'] );

Takes a check definition hash and paramters and returns true if the check should be run. Used by "check" to determine which checks to run.

Supported parameters:

tags

Tags can be either "positive" or "negative". A negative tag is indicated by a leading !. A check is run if its tags match any of the passed in positive tags and none of the negative ones. If no tags are passed in, all checks will be run.

If the invocant can('tags') and there are no tags in the "full hashref of params" then the return value of that method is used.

If a check has no tags defined, will use the default tags defined when the object was created.

DEPENDENCIES

Perl 5.10 or higher.

CONFIGURATION AND ENVIRONMENT

None

SEE ALSO

HealthCheck::Diagnostic

The GSG Health Check Standard.

AUTHOR

Grant Street Group <developers@grantstreet.com>

COPYRIGHT AND LICENSE

This software is Copyright (c) 2017 - 2020 by Grant Street Group.

This is free software, licensed under:

  The Artistic License 2.0 (GPL Compatible)