Running stand-alone

    $ plackup bin/app.psgi
    HTTP::Server::PSGI: Accepting connections at http://0:5000/

Point your browser at it, and away you go!

This option can be useful for small personal web apps or internal apps, but if you want to make your app available to the world, it probably won't suit you.

Auto Reloading the Application

While developing your application, it is often handy to have the server automatically reload your application when changes are made. There are two recommended ways of handling this with Dancer: using " plackup -r " and Plack::Loader::Shotgun. Both have their advantages and disadvantages (which will be explained below).

Regardless of the method you use, it is not recommended that you automatically reload your applications in a production environment, for reasons of performance, deployment best practices, etc.

For Dancer 1 programmers that used the " auto_reload " option, please use one of these alternatives instead:

Auto reloading with " plackup -r "

Plack's built-in reloader will reload your application anytime a file in your application's directory (usually, /bin ) changes. You will likely want to monitor your lib/ directory too, using the " -R " option:

    $ plackup -r -R lib bin/app.psgi

There is a performance hit associated with this, as Plack will spin off a separate process that monitors files in the application and other specified directories. If the timestamp of any files in a watched directory changes, the application is recompiled and reloaded.

See the plackup docs for more information on the " -r " and " -R " options.

Auto reloading with plackup and Shotgun

There may be circumstances where Plack's built-in reloader won't work for you, be it for the way it looks for changes, or because there are many directories you need to monitor, or you want to reload the application any time one of the modules in Perl's lib/ path changes. Plack::Loader::Shotgun makes this easy by recompiling the application on every request.

To use Shotgun, specify it using the loader argument to " plackup (-L) ":

    $ plackup -L Shotgun bin/app.psgi

The Shotgun, while effective, can quickly cause you performance issues, even during the development phase of your application. As the number of plugins you use in your application grows, as the number of static resources (images, etc.) grows, the more requests your server process needs to handle. Since each request recompiles the application, even simple page refreshes can get unbearably slow over time. Use with caution.

You can bypass Shotgun's auto-reloading of specific modules with the " -M " switch:

    $ plackup -L Shotgun -M<MyApp::Foo> -M<MyApp::Bar> bin/app.psgi

On Windows, Shotgun loader is known to cause huge memory leaks in a fork-emulation layer. If you are aware of this and still want to run the loader, please use the following command:

    > set PLACK_SHOTGUN_MEMORY_LEAK=1 && plackup -L Shotgun bin\app.psgi
    HTTP::Server::PSGI: Accepting connections at http://0:5000/

Please note: if you are using Dancer 2's asynchronous capabilities, using Shotgun will kill Twiggy. If you need async processing, consider an alternative to Shotgun.

Running under Apache

As a CGI script

In its simplest form, your Dancer app can be run as a simple CGI script out-of-the-box. You will need to enable the Apache mod_cgi or mod_cgid modules ("a2enmod cgi" or "a2enmod cgid" on Debian-based systems) and mod_rewrite ("a2enmod rewrite"). The Perl module Plack::Runner is required.

The following is an example apache configuration. Depending on your Apache configuration layout, this should be placed in "httpd.conf" or "sites-available/*site*". The configuration options can also be placed in ".htaccess" files if you prefer.

    <VirtualHost *:80>
        ServerName www.example.com

        # /srv/www.example.com is the root of your
        # dancer application
        DocumentRoot /srv/www.example.com/public

        ServerAdmin you@example.com

        <Directory "/srv/www.example.com/public">
            AllowOverride None
            Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
            AddHandler cgi-script .cgi
            # Apache 2.2
            Order allow,deny
            Allow from all
            # Apache 2.4
            Require all granted
        </Directory>

        RewriteEngine On
        RewriteCond %{REQUEST_FILENAME} !-f
        RewriteRule ^(.*)$ /dispatch.cgi$1 [QSA,L]

        ErrorLog  /var/log/apache2/www.example.com-error.log
        CustomLog /var/log/apache2/www.example.com-access_log common
    </VirtualHost>

Now you can access your dancer application URLs as if you were using the embedded web server.

    http://www.example.com/

This option is a no-brainer, easy to setup and low maintenance, but serves requests slower than all other options, as each time a request is made to your server, Apache will start your application. This might be suitable for a small, occasionally-used sites, as the application is not using resources when it is not being accessed. For anything more, you probably want to use FastCGI instead (see next section).

To list all currently loaded modules, type "apachectl -M" ("apache2ctl -M" on Debian/Ubuntu).

As a FastCGI script

This has all the easy-to-setup and low-maintenance advantages of CGI, but is much faster for each request, as it keeps a copy of the application running all the time.

You will still need to enable "mod_rewrite", but will need to use a FastCGI module instead of a CGI module. There are 3 available: mod_fcgid <http://httpd.apache.org/mod_fcgid/>, mod_fastcgi <http://www.fastcgi.com/> and mod_proxy_fcgi <https://httpd.apache.org/docs/trunk/mod/mod_proxy_fcgi.html>. For this example, we will use mod_fastcgi ("a2enmod fastcgi" in Debian).

The CGI configuration above now changes as follows (differences highlighted with XXX):

    <VirtualHost *:80>
        ServerName www.example.com

        # /srv/www.example.com is the root of your
        # dancer application
        DocumentRoot /srv/www.example.com/public

        ServerAdmin you@example.com

        # XXX Start a FastCGI server to run in the background
        FastCgiServer /srv/www.example.com/public/dispatch.fcgi

        <Directory "/srv/www.example.com/public">
            AllowOverride None
            Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
            # XXX Use FastCGI handler instead of CGI
            AddHandler fastcgi-script .fcgi
            # Apache 2.2
            Order allow,deny
            Allow from all
            # Apache 2.4
            Require all granted
        </Directory>

        RewriteEngine On
        RewriteCond %{REQUEST_FILENAME} !-f
        # Run FastCGI dispatcher instead of CGI dispatcher
        RewriteRule ^(.*)$ /dispatch.fcgi$1 [QSA,L]

        ErrorLog  /var/log/apache2/www.example.com-error.log
        CustomLog /var/log/apache2/www.example.com-access_log common
    </VirtualHost>

This is the easiest way to get a production server up and running, as there is no need to worry about daemonizing your application. Apache manages all that for you.

Reloading your application

You can use "apache2ctl restart" or "apache2ctl graceful" to reload your application. The latter will be more friendly to your users in a production environment. If your application loads relatively quickly, then it should go unnoticed.

Configuration

See <http://www.fastcgi.com/mod_fastcgi/docs/mod_fastcgi.html> for FastCGI configuration options. An example configuration:

   FastCgiServer /srv/www.example.com/public/dispatch.fcgi -processes 5 -initial-env DANCER_ENVIRONMENT="production"

With Plack

You can run your app from Apache using PSGI (Plack), with a config like the following:

    <VirtualHost myapp.example.com>
        ServerName www.myapp.example.com
        ServerAlias myapp.example.com
        DocumentRoot /websites/myapp.example.com

        <Directory /home/myapp/myapp>
            AllowOverride None
            Order allow,deny
            Allow from all
        </Directory>

        <Location />
            SetHandler perl-script
            PerlResponseHandler Plack::Handler::Apache2
            PerlSetVar psgi_app /websites/myapp.example.com/app.psgi
        </Location>

        ErrorLog  /websites/myapp.example.com/logs/error_log
        CustomLog /websites/myapp.example.com/logs/access_log common
    </VirtualHost>

To set the environment you want to use for your application (production or development), you can set it this way:

    <VirtualHost>
        ...
        SetEnv DANCER_ENVIRONMENT "production"
        ...
    </VirtualHost>

Running multiple applications under the same virtualhost

If you want to deploy multiple applications under the same "VirtualHost" (using one application per directory, for example) you can use the following example Apache configuration.

This example uses the FastCGI dispatcher that comes with Dancer, but you should be able to adapt this to use any other way of deployment described in this guide. The only purpose of this example is to show how to deploy multiple applications under the same base directory/virtualhost.

    <VirtualHost *:80>
        ServerName localhost
        DocumentRoot "/path/to/rootdir"
        RewriteEngine On
        RewriteCond %{REQUEST_FILENAME} !-f

        <Directory "/path/to/rootdir">
            AllowOverride None
            Options +ExecCGI -MultiViews +SymLinksIfOwnerMatch
            Order allow,deny
            Allow from all
            AddHandler fastcgi-script .fcgi
        </Directory>

        RewriteRule /App1(.*)$ /App1/public/dispatch.fcgi$1 [QSA,L]
        RewriteRule /App2(.*)$ /App2/public/dispatch.fcgi$1 [QSA,L]
        ...
        RewriteRule /AppN(.*)$ /AppN/public/dispatch.fcgi$1 [QSA,L]
    </VirtualHost>

Of course, if your Apache configuration allows that, you can put the RewriteRules in a .htaccess file directly within the application's directory, which lets you add a new application without changing the Apache configuration.

Running on PSGI-based Perl webservers

Starman

"Starman" is a high performance web server, with support for preforking, signals, multiple interfaces, graceful restarts and dynamic worker pool configuration.

Twiggy

"Twiggy" is an "AnyEvent" web server, it's light and fast.

Corona

"Corona" is a "Coro" based web server.

Similar to running standalone, use plackup to start your application (see Plack and specific servers above for all available options):

    $ plackup bin/app.psgi
    $ plackup -E deployment -s Starman --workers=10 -p 5001 -a bin/app.psgi

As you can see, the scaffolded Perl script for your app can be used as a PSGI startup file.

Enabling content compression

Content compression (gzip, deflate) can be easily enabled via a Plack middleware (see "Plack::Middleware" in Plack): Plack::Middleware::Deflater. It's a middleware to encode the response body in gzip or deflate, based on the "Accept-Encoding" HTTP request header.

Enable it as you would enable any Plack middleware. First you need to install Plack::Middleware::Deflater, then in the handler (usually app.psgi) edit it to use Plack::Builder, as described above:

    use Dancer2;
    use MyWebApp;
    use Plack::Builder;

    builder {
        enable 'Deflater';
        dance;
    };

To test if content compression works, trace the HTTP request and response before and after enabling this middleware. Among other things, you should notice that the response is gzip or deflate encoded, and contains a header "Content-Encoding" set to "gzip" or "deflate".

Creating a service

You can turn your app into proper service running in background using one of the following examples:

Using Ubic

Ubic is an extensible perlish service manager. You can use it to start and stop any services, automatically start them on reboots or daemon failures, and implement custom status checks.

A basic PSGI service description (usually in "/etc/ubic/service/application"):

    use parent qw(Ubic::Service::Plack);

    # if your application is not installed in @INC path:
    sub start {
        my $self = shift;
        $ENV{PERL5LIB} = '/path/to/your/application/lib';
        $self->SUPER::start(@_);
    }

    __PACKAGE__->new(
        server => 'Starman',
        app => '/path/to/your/application/app.psgi',
        port => 5000,
        user => 'www-data',
    );

Run "ubic start application" to start the service.

Using daemontools

daemontools is a collection of tools for managing UNIX services. You can use it to easily start/restart/stop services.

A basic script to start an application: (in "/service/application/run")

    #!/bin/sh

    # if your application is not installed in @INC path:
    export PERL5LIB='/path/to/your/application/lib'

    exec 2>&1 \
    /usr/local/bin/plackup -s Starman -a /path/to/your/application/app.psgi -p 5000

Running stand-alone behind a proxy / load balancer

    behind_proxy: 1

This setup can be achieved using various software; examples would include:

Using Apache's mod_proxy

You could set up a "VirtualHost" for your web app, and proxy all requests through to it:

    <VirtualHost mywebapp.example.com:80>
    ProxyPass / http://localhost:3000/
    ProxyPassReverse / http://localhost:3000/
    </VirtualHost>

Or, if you want your webapp to share an existing VirtualHost, you could have it under a specified dir:

    ProxyPass /mywebapp/ http://localhost:3000/
    ProxyPassReverse /mywebapp/ http://localhost:3000/

It is important for you to note that the Apache2 modules "mod_proxy" and "mod_proxy_http" must be enabled:

    $ a2enmod proxy
    $ a2enmod proxy_http

It is also important to set permissions for proxying for security purposes, below is an example.

    <Proxy *>
      Order allow,deny
      Allow from all
    </Proxy>

Using perlbal

"Perlbal" is a single-threaded event-based server written in Perl supporting HTTP load balancing, web serving, and a mix of the two, available from <http://www.danga.com/perlbal/>

It processes hundreds of millions of requests a day just for LiveJournal, Vox and TypePad and dozens of other "Web 2.0" applications.

It can also provide a management interface to let you see various information on requests handled etc.

It could easily be used to handle requests for your Dancer apps, too.

It can be easily installed from CPAN:

    perl -MCPAN -e 'install Perlbal'

Once installed, you'll need to write a configuration file. See the examples provided with perlbal, but you'll probably want something like:

    CREATE POOL my_dancers
    POOL my_dancers ADD 10.0.0.10:3030
    POOL my_dancers ADD 10.0.0.11:3030
    POOL my_dancers ADD 10.0.0.12:3030
    POOL my_dancers ADD 10.0.0.13:3030

    CREATE SERVICE my_webapp
    SET listen          = 0.0.0.0:80
    SET role            = reverse_proxy
    SET pool            = my_dancers
    SET persist_client  = on
    SET persist_backend = on
    SET verify_backend  = on
    ENABLE my_webapp

Using balance

"balance" is a simple load-balancer from Inlab Software, available from <http://www.inlab.de/balance.html>.

It could be used simply to hand requests to a standalone Dancer app. You could even run several instances of your Dancer app, on the same machine or on several machines, and use a machine running "balance" to distribute the requests between them, for some serious heavy traffic handling!

To listen on port 80, and send requests to a Dancer app on port 3000:

    balance http localhost:3000

To listen on a specified IP only on port 80, and distribute requests between multiple Dancer apps on multiple other machines:

    balance -b 10.0.0.1 80 10.0.0.2:3000 10.0.0.3:3000 10.0.0.4:3000

Using Lighttpd

You can use Lighttpd's "mod_proxy":

    $HTTP["url"] =~ "/application" {
        proxy.server = (
            "/" => (
                "application" => ( "host" => "127.0.0.1", "port" => 3000 )
            )
        )
    }

This configuration will proxy all request to the /application path to the path / on localhost:3000.

Using Nginx

with Nginx:

    upstream backendurl {
        server unix:THE_PATH_OF_YOUR_PLACKUP_SOCKET_HERE.sock;
    }

    server {
      listen       80;
      server_name YOUR_HOST_HERE;

      access_log /var/log/YOUR_ACCESS_LOG_HERE.log;
      error_log  /var/log/YOUR_ERROR_LOG_HERE.log info;

      root YOUR_ROOT_PROJECT/public;
      location / {
        try_files $uri @proxy;
        access_log off;
        expires max;
      }

      location @proxy {
            proxy_set_header Host $http_host;
            proxy_set_header X-Forwarded-Host $host;
            proxy_set_header X-Real-IP $remote_addr;
            proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
            proxy_pass       http://backendurl;
      }

    }

You will need plackup to start a worker listening on a socket :

    cd YOUR_PROJECT_PATH
    sudo -u www plackup -E production -s Starman --workers=2 -l THE_PATH_OF_YOUR_PLACKUP_SOCKET_HERE.sock -a bin/app.pl

A good way to start this is to use "daemontools" and place this line with all environments variables in the "run" file.

Using HAProxy

"HAProxy" is a reliable high-performance TCP/HTTP load balancer written in C available from <https://www.haproxy.org/>.

Suppose we want to run an application at "app.example.com:80" and would to use two backends listen on hosts "app-be1.example.com:3000" and "app-be2.example.com:3000".

Here is HAProxy configuration file (haproxy.conf):

    global
        nbproc  1
        maxconn 4096
        user    nobody
        group   nobody
        # haproxy logs will be collected by syslog
        # syslog: unix socket path or tcp pair (ipaddress:port)
        log     /var/run/log local0
        daemon
        # enable compression (haproxy v1.5-dev13 and above required)
        tune.comp.maxlevel  5

    defaults
        log     global
        option  httpclose
        option  httplog
        option  dontlognull
        option  forwardfor
        option  abortonclose
        mode    http
        balance roundrobin
        retries 3
        timeout connect         5s
        timeout server          30s
        timeout client          30s
        timeout http-keep-alive 200m
        # enable compression (haproxy v1.5-dev13 and above required)
        compression algo gzip
        compression type text/html application/javascript text/css application/x-javascript text/javascript

    # application frontend (available at http://app.example.com)
    frontend app.example.com
        bind                  :80
        # modify request headers
        reqadd                X-Forwarded-Proto:\ http
        reqadd                X-Forwarded-Port:\ 80
        # modify response headers
        rspdel                ^Server:.*
        rspdel                ^X-Powered-By:.*
        rspadd                Server:\ Dethklok\ (Unix/0.2.3)
        rate-limit sessions   1024
        acl is-haproxy-stats  path_beg /stats
        # uncomment if you'd like to get haproxy usage statistics
        # use_backend haproxy   if is-haproxy-stats
        default_backend       dynamic

    # haproxy statistics (available at http://app.example.com/stats)
    backend haproxy
        stats uri             /stats
        stats refresh         180s
        stats realm           app.example.com\ haproxy\ statistics
        # change credentials
        stats auth            admin1:password1
        stats auth            admin2:password2
        stats hide-version
        stats show-legends

    # application backends
    backend dynamic
        # change path_info to check and value of the Host header sent to application server
        option httpchk HEAD / HTTP/1.1\r\nHost:\ app.example.com
        server app1 app-be1.example.com:3000 check inter 30s
        server app2 app-be2.example.com:3000 check inter 30s

We will need to start the workers on each backend of our application. This can be done by starman utility:

    # on app-be1.example.com
    $ starman --workers=2 --listen :3000 /path/to/app.pl
    # on app-be2.example.com
    $ starman --workers=2 --listen :3000 /path/to/app.pl

Then start the haproxy itself:

    # check the configuration..
    $ sudo haproxy -c -f haproxy.conf
    # now really start it..
    $ sudo haproxy -f haproxy.conf

Running on lighttpd

To run as a CGI app on lighttpd, just create a soft link to the "dispatch.cgi" script (created when you run "dancer -a MyApp") inside your system's "cgi-bin" folder. Make sure "mod_cgi" is enabled.

    ln -s /path/to/MyApp/public/dispatch.cgi /usr/lib/cgi-bin/mycoolapp.cgi

Running on lighttpd (FastCGI)

Make sure "mod_fcgi" is enabled. You also must have FCGI installed.

This example configuration uses TCP/IP:

    $HTTP["url"] == "^/app" {
        fastcgi.server += (
            "/app" => (
                "" => (
                    "host" => "127.0.0.1",
                    "port" => "5000",
                    "check-local" => "disable",
                )
            )
        )
    }

Launch your application:

    plackup -s FCGI --port 5000 bin/app.psgi

This example configuration uses a socket:

    $HTTP["url"] =~ "^/app" {
        fastcgi.server += (
            "/app" => (
                "" => (
                    "socket" => "/tmp/fcgi.sock",
                    "check-local" => "disable",
                )
            )
        )
    }

Launch your application:

    plackup -s FCGI --listen /tmp/fcgi.sock bin/app.psgi

Performance Improvements

• CGI::Deurl::XS
• Class::XSAccessor
• Cpanel::JSON::XS
• Crypt::URandom
• HTTP::XSCookies
• HTTP::XSHeaders
• Math::Random::ISAAC::XS
• MooX::TypeTiny
• Type::Tiny::XS
• URL::Encode::XS
• YAML::XS

If you generated your application with "dancer2 gen", you can easily install these with the following command:

    cpanm --installdeps . --with-feature=accelerate

To build them, you will need access to a C compiler, and using these modules will prevent you from fatpacking your application.

These modules are installed by default when building a Docker container containing your application.