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Dancer2-1.1.0
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/ Dancer2::Manual::Deployment

NAME

Dancer2::Manual::Deployment - common ways to put your Dancer app into use

VERSION

version 1.1.0

DESCRIPTION

Dancer has been designed to be flexible, and this flexibility extends to your choices when deploying your Dancer app.

Running stand-alone

To start your application, just run plackup:

$ 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

You can run your Dancer app from Apache using the following examples:

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, mod_fastcgi and mod_proxy_fcgi. 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

A number of Perl web servers supporting PSGI are available on cpan:

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

Another option would be to run your app stand-alone as described above, but then use a proxy or load balancer to accept incoming requests (on the standard port 80, say) and feed them to your Dancer app. Also, in this case you might want to look at the behind_proxy configuration option, to make sure that all the URLs are constructed properly.

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

Running on lighttpd (CGI)

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

The following modules can be used to speed up an app in Dancer2:

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.

AUTHOR

Dancer Core Developers

COPYRIGHT AND LICENSE

This software is copyright (c) 2023 by Alexis Sukrieh.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.