Decongestion potential bottlenecks on trivial_rewrite(8).

Which might be caused by slow LDAP lookups in transport_maps.  Instead,
we alias each addresses for which we want a custom transport to a
dedicated "dummy" domain, and use a static (CDB) transport_maps to map
said domains to their transport;  the receiver can then use canonical(8)
to restore the original envelope recipient.  Since the alias resolution
is performed by cleanup(8), which can run in parallel with other
instances, it should decongestion bottlenecks under heavy loads.

So far only the MX:es have been decongestioned.  The list manager and
the MDA should be treated as well.

3 files changed, 15 insertions, 0 deletions

diff --git a/roles/IMAP/files/etc/postfix/recipient_canonical.pcre b/roles/IMAP/files/etc/postfix/recipient_canonical.pcre
new file mode 100644
index 0000000..07c5859
--- /dev/null
+++ b/roles/IMAP/files/etc/postfix/recipient_canonical.pcre
@@ -0,0 +1,4 @@
+# Restore the original envelope recipient (drop our internal domain).
+# Extensions are preserved as they are included in $2.
+
+/^([^\/]+)\/(.+)@[^@]+$/    $2@$1
diff --git a/roles/IMAP/tasks/mda.yml b/roles/IMAP/tasks/mda.yml
index 1aac519..0358f12 100644
--- a/roles/IMAP/tasks/mda.yml
+++ b/roles/IMAP/tasks/mda.yml
@@ -12,25 +12,31 @@
   register: r
   notify:
     - Restart Postfix
 
 - name: Create directory /etc/postfix-.../virtual
   file: path=/etc/postfix-{{ postfix_instance[inst].name }}/virtual
         state=directory
         owner=root group=root
         mode=0755
 
 - name: Copy lookup tables
   copy: src=etc/postfix/virtual/{{ item }}
         dest=/etc/postfix-{{ postfix_instance[inst].name }}/virtual/{{ item }}
         owner=root group=root
         mode=0644
   with_items:
     - mailbox_domains.cf
     - mailbox.cf
     - transport_content_filter.cf
 
+- name: Copy recipient canonical
+  copy: src=etc/postfix/recipient_canonical.pcre
+        dest=/etc/postfix-{{ postfix_instance[inst].name }}/recipient_canonical.pcre
+        owner=root group=root
+        mode=0644
+
 - name: Start Postfix
   service: name=postfix state=started
   when: not r.changed
 
 - meta: flush_handlers
diff --git a/roles/IMAP/templates/etc/postfix/main.cf.j2 b/roles/IMAP/templates/etc/postfix/main.cf.j2
index e4c01bd..d0421ce 100644
--- a/roles/IMAP/templates/etc/postfix/main.cf.j2
+++ b/roles/IMAP/templates/etc/postfix/main.cf.j2
@@ -38,24 +38,29 @@ inet_protocols   = ipv4
 mydestination        =
 local_transport      = error:5.1.1 Mailbox unavailable
 alias_maps           =
 alias_database       =
 local_recipient_maps =
 
 message_size_limit  = 67108864
 recipient_delimiter = +
 
 # No relay: this server is inbound-only
 relay_transport   = error:5.1.1 Relay unavailable
 default_transport = error:5.1.1 Transport unavailable
 
 # Virtual transport (the alias resolution is already done by the MX:es)
 virtual_transport       = lmtp:unix:private/dovecot-lmtpd
 lmtp_bind_address       = 127.0.0.1
 virtual_mailbox_domains = ldap:$config_directory/virtual/mailbox_domains.cf
 virtual_mailbox_maps    = ldap:$config_directory/virtual/mailbox.cf
 transport_maps          = ldap:$config_directory/virtual/transport_content_filter.cf
 
+# Restore the original envelope recipient
+relay_domains               = $myhostname
+recipient_canonical_classes = envelope_recipient
+recipient_canonical_maps    = pcre:$config_directory/recipient_canonical.pcre
+
 # Don't rewrite remote headers
 local_header_rewrite_clients =
 # Tolerate occasional high latency
 smtpd_timeout                = 1200s