[dancer-users] Passing environment to dockerized Dancer2

[Mikko Johannes Koivunalho]

> Dear Dancer users,
>
> I want to run my Dancer2 application in a docker but I want to run the
> docker without mounting any local directories and I want to run the same
> container in all environments, not compile it separately for different
> environments.
>
> Problem:
> How do I pass the environment dependent parts of the configuration to
> the docker? I cannot use file `config_local.yaml` because then I would
> need to copy that file somehow into the container when it starts.
>
> Possible solution:
> I would pass parts of the configuration as environment variables, e.g.
> /DB_HOST/  and/SITE_URL/, and then apply these over the values in
> config.yaml when I am creating the endpoints.
>
> Suggestion:
> Change the command `/config/` (or the underlying file reader function)
> so that it can transpose environment variables into config strings, e.g.
> plugins->database->connections->main->host = '${DB_HOST}'.

I have built a solution to this.
I have not yet submitted a Pull Request.
I am using this solution in my build and web application.
Please comment. Would this be a good pull request?

What the PR does?

1) After reading the whole config from different files, it traverses the 
whole tree and if it sees a string with a substring like 
"${ENV:SOME_ENV}", it changes it to the corresponding environment 
variable, if that environment variable is defined.
2) Before doing 1), it checks if the config item "env_var_replace" is 
defined and is boolean true. If so, then it executes 1). Otherwise it 
skips. This is to maintain backwards compatibility.

(I have tests for the actual PR. Not included here.)


diff --git a/lib/Dancer2/Core/Role/ConfigReader.pm 
b/lib/Dancer2/Core/Role/ConfigReader.pm
index 0d0bc1ab..b8e1fdaf 100644
--- a/lib/Dancer2/Core/Role/ConfigReader.pm
+++ b/lib/Dancer2/Core/Role/ConfigReader.pm
@@ -232,6 +232,12 @@ sub load_config_file {
      }

      # TODO handle mergeable entries
+
+    if( defined $config->{'env_var_replace'} && 
$config->{'env_var_replace'} ) {
+        warn "Apply environment variables to config\n" if 
$ENV{DANCER_CONFIG_VERBOSE};
+        $self->_replace_env_vars($config);
+    }
+
      return $config;
  }

@@ -275,6 +281,48 @@ sub _compile_config_entry {
      return $trigger->( $self, $value, $config );
  }

+# Attn. We are traversing along the original data structure all the time,
+# using references, and changing values on the spot, not returning 
anything.
+sub _replace_env_vars {
+    my ( $self, $entry ) = @_;
+    if( ref $entry ne 'HASH' && ref $entry ne 'ARRAY' ) {
+        croak 'Param entry is not HASH or ARRAY';
+    }
+    if( ref $entry eq 'HASH' ) {
+        foreach my $value (values %{ $entry }) {
+            if( (ref $value) =~ m/(HASH|ARRAY)/msx ) {
+                $self->_replace_env_vars( $value );
+            } elsif( (ref $value) =~ m/(CODE|REF|GLOB)/msx ) {
+                # Pretty much anything else except SCALAR. Do nothing
+                1;
+            } else {
+                if( $value ) {
+                    while( my ($k, $v) = each %ENV) {
+                        $value =~ s/ \$ [{] ENV:$k [}] /$v/gmsx;
+                    }
+                }
+            }
+        }
+    } else {
+        # ref $entry is 'ARRAY'
+        foreach my $value (@{ $entry }) {
+            if( (ref $value) =~ m/(HASH|ARRAY)/msx ) {
+                $self->_replace_env_vars( $value );
+            } elsif( (ref $value) =~ m/(CODE|REF|GLOB)/msx ) {
+                # Pretty much anything else except SCALAR. Do nothing
+                1;
+            } else {
+                if( $value ) {
+                    while( my ($k, $v) = each %ENV) {
+                        $value =~ s/ \$ [{] ENV:$k [}] /$v/gmsx;
+                    }
+                }
+            }
+        }
+    }
+    return;
+}
+
  1;

  __END__



-- 
Mikko Koivunalho
LinkedIn: http://www.linkedin.com/in/MikkoKoivunalho
AboutMe: http://about.me/mikkokoivunalho
Blog: http://www.koivunalho.org/blogs/exercises-in-integration-and-delivery/