diff --git a/03-developer-how-to-for-modules.md b/03-developer-how-to-for-modules.md
index 0519a5e2d33758af8c294665e1cdfaa138b102e0..58b7d1142c11afc5b9ab1ce0905f890193c73c06 100644
--- a/03-developer-how-to-for-modules.md
+++ b/03-developer-how-to-for-modules.md
@@ -631,3 +631,41 @@ To uninstall, just:
 ```bash
 python3 -m pip uninstall osmclient
 ```
+
+## kafka messages
+
+OSM modules interchange messages via kafka. Each message is composed by a topic, a key and a value..
+
+Used **kafka topics** at OSM are: (in brakets is indicated modules that produce and consume them with the following leyend: [P: producer] [Ca: consumer by all instances, that is broadcasted] [C: consumer only by one instance, that is load balanced]):
+
+- admin: [P: NBI,LCM] [Ca: NBI,LCM] administrative or OSM internal issues
+- vnfd: [P: NBI] related to vnf descriptor
+- nsd: [P: NBI] related to ns descriptor
+- nst: [P: NBI] related to netslice template
+- pdu: [P: NBI] realted to physical data units
+- ns: [P: NBI] [C: NBI,LCM] related to network service
+- nsi: [P: NBI] [C: NBI,LCM] related to netslice instance
+- vim_account: [P: NBI] [C: LCM] related to VIM target
+- wim_account: [P: NBI] [C: LCM] related to WIM target
+- sdn: [P: NBI] [C: LCM] related to Software Define Network Controller
+- k8scluster: [P: NBI] [C: LCM] related to kubernetes cluster
+- k8srepo: [P: NBI] [C: LCM] related to kubernetes repository
+- pla: [P: LCM] [C: LCM] related to placement location algorithm
+- user: [P: NBI] related to OSM user
+- project: [P: NBI] related to OSM user
+
+Used **kafka keys** are topic dependent, but common keys include and action to do (infinitive), or an action already done (past partiple):
+
+- create/created: to create/has been created
+- delete/deleted: to delete/has been deleted
+- edit/edited: to update or change/has been updated or changed
+- instantiate/instantiated: to instantiate a `ns` or `nsi`
+- terminate/terminated: to remove the instantiation of a `ns` or `nsi`
+- scale/scaled: to scale a `ns` or `nsi`
+- action/actioned: to perform a day-2 operation over a `ns` or `nsi`
+- ping: used for `admin` just to sent a keep alive
+- echo: used for `admin` for debuging and kakfa initialization. Receiver just log the content
+- revoke_token: used for `admin` at NBI to inform other peers to clean the token cache of one or all
+- get_placement/placement: used for `pla` to order a new placement calculation/receive a placement result
+
+The content of kafka **values** are a dictionary, except for `echo` key that is  a text. Dictionary contains at least the `_id` key (OSM identifier) needed for identigy  the target element in the database. In the case of ns/nsi it contains also the operation id (`nslcmop_id`/`nsilcmop_id`).