erp5: Improve replication setup support.

Document how to setup replication.
Add support for no-zope ERP5 instance, so it is possible to setup a
replicating, full-featured ERP5 Cluster instance tree without providing
service until it needs to take over its upstream, or to become
otherwise independent.

software/erp5/README.rst

@@ -4,7 +4,7 @@ Available ``software-type`` values
 - ``default``
 
   Recommended for production use.
-  
+
 - ``create-erp5-site``
 
   Automated creation of ERP5Site instance, for easy deployment.
@@ -22,6 +22,62 @@ Included cloudooo partition is **deprecated**. It is not recommended for
 intensive usage. See the ``cloudooo`` Software Release to setup a cloudooo
 cluster, more suitable for intensive usage.
 
+Replication
+===========
+
+Replication allows setting up an ERP5 instance whose data follows another
+instance.
+
+Relations between ERP5 instances in a replication graph depend in what is
+supported by individual data managers (ex: a neo cluster can replicate from a
+neo cluster which itself replicates from a 3rd).
+
+Replication lag constraints (aka sync/async replication) depends on individual
+data managers (ex: neo replication between clusters is always asynchronous).
+
+Ignoring replication lag, replicated data can be strictly identical (ex:
+replicating ZODB or SQL database will contain the same data as upstream), or
+may imply some remaping (ex: replicating Zope logs from an instance with 2 zope
+families with 2 partition of 2 zopes each to an instance with a single zope
+total).
+
+Data whose replication is supported
+-----------------------------------
+
+- neo database
+
+Data whose replication will eventually be supported
+---------------------------------------------------
+
+- mariadb database
+- zope ``zope-*-access.log`` and ``zope-*-Z2.log``
+- ``mariadb-slow.log``
+
+Data whose replication is not planned
+-------------------------------------
+
+- zeo: use neo instead
+
+Setting up replication
+----------------------
+
+In addition to your usual parameter set, you needs to provide the following parameters::
+
+  {
+    "zope-partition-dict": {},      So no zope is instanciated
+    "zodb": [
+      {
+        "storage-dict": {
+          "upstream-masters": ...,  As published by to-become upstream ERP5 instance as "neo-masters"
+        },
+        "type": "neo",              The only ZODB type supporting replication
+        ...
+      }
+      ...
+    ]
+    ...
+  }
+
 Port ranges
 ===========
 

stack/erp5/buildout.cfg

@@ -331,7 +331,7 @@ rendered = ${monitor-template-dummy:target}
 [template-erp5]
 <= download-base
 filename = instance-erp5.cfg.in
-md5sum = 66edf64eeaecded8977459acb26f4424
+md5sum = cb0a8dfc15874939ec786a8b7ac5bff1
 
 [template-zeo]
 <= download-base

stack/erp5/instance-erp5.cfg.in

@@ -117,6 +117,10 @@ name = neo-${gen-neo-cluster-base:passwd}
 [gen-smtpd-sasl-password]
 < = gen-password
 
+{% set zope_partition_dict = slapparameter_dict.get('zope-partition-dict', {'1': {}}) -%}
+{% set zope_address_list_id_dict = {} -%}
+{% if zope_partition_dict -%}
+
 [request-zope-base]
 <= request-common
 return =
@@ -158,7 +162,7 @@ software-type = zope
 
 {% set zope_family_dict = {} -%}
 {% set jupyter_zope_family_default = [] -%}
-{% for custom_name, zope_parameter_dict in slapparameter_dict.get('zope-partition-dict', {'1': {}}).items() -%}
+{% for custom_name, zope_parameter_dict in zope_partition_dict.items() -%}
 {%   set partition_name = 'zope-' ~ custom_name -%}
 {%   set section_name = 'request-' ~ partition_name -%}
 {%   set zope_family = zope_parameter_dict.get('family', 'default') -%}
@@ -189,7 +193,6 @@ config-webdav = {{ dumps(zope_parameter_dict.get('webdav', False)) }}
 {% endif -%}
 
 {# We need to concatenate lists that we cannot read as lists, so this gets hairy. -#}
-{% set zope_address_list_id_dict = {} -%}
 {% set zope_family_parameter_dict = {} -%}
 {% for family_name, zope_section_id_list in zope_family_dict.items() -%}
 {%   for zope_section_id in zope_section_id_list -%}
@@ -264,6 +267,8 @@ config-{{ name }} = {{ value }}
 return = site_url
 {% endif -%}
 
+{% endif -%}{# if zope_partition_dict -#}
+
 [publish]
 recipe = slapos.cookbook:publish.serialised
 -extends = publish-early
@@ -271,11 +276,13 @@ recipe = slapos.cookbook:publish.serialised
 neo-masters = ${neo-0-final:connection-masters}
 neo-admins = ${neo-0-final:connection-admins}
 {% endif  -%}
+{% if zope_address_list_id_dict -%}
 {#
 Pick any published hosts-dict, they are expected to be identical - and there is
 no way to check here.
 -#}
 hosts-dict = {{ '${' ~ zope_address_list_id_dict.keys()[0] ~ ':connection-hosts-dict}' }}
+{% endif -%}
 {% for name, value in publish_dict.items() -%}
 {{   name }} = {{ value }}
 {% endfor -%}