OTA-2294: Update doc with details on running multiple IP secondaries

Signed-off-by: Mike Sul <ext-mykhaylo.sul@here.com>

docs/posix-secondaries-bitbaking.adoc

@@ -1,6 +1,6 @@
 = Posix Secondaries: bitbaking and usage of Primary and Secondary images
 
-The goal of this doc is to guide a reader on bitbaking of two type of images `primary` and `secondary` that are targeted for QEMU (and RPi TBD)
+The goal of this doc is to guide a reader on bitbaking of two type of images `primary` and `secondary` that are targeted for QEMU or RPi
 and running of which on the target makes it act as `Primary` and `Secondary` ECU of a single device.
 
 Please, refer to link:https://uptane.github.io/uptane-standard/uptane-standard.html[the Uptane standard] in order to grok the meaning of the `Primary` and `Secondary` terms in the given context from a theoretical standpoint.
@@ -45,6 +45,9 @@ bitbake primary-image
 | A space separated list of TCP/IP addresses of the Secondaries to be included into the list of ECUs served by the given Primary
 |===
 
+Please, note that PRIMARY_SECONDARIES can be a list of TCP/IP addresses in order to fulfill multiple secondaries use case.
+For example, `PRIMARY_SECONDARIES = "10.0.3.2:9050 10.0.3.3:9050 10.0.3.4:9050"`.
+
 
 === Secondary
 To bitbake an image for `Secondary` run the following
@@ -66,6 +69,21 @@ bitbake secondary-image
 |A TCP port that Secondary listen on for connections from Primary
 |===
 
+==== Multiple secondaries use case
+In order to support multiple secondaries use case an user should
+
+* repeat the secondary bitbaking procedure corresponding number of times, each time
+** specifying unique TCP/IP address by means of `SECONDARY_IP` and `SECONDARY_PORT` configuration variables
+** copying and naming uniquely the resultant image file (e.g. `cp tmp/deploy/images/qemux86-64/secondary-image-qemux86-64.ota-ext4 secondary-images/secondary-image-qemux86-64.ota-ext4-001`)
+* bitbake the primary image with `PRIMARY_SECONDARIES` listing the corresponding secondaries TCP/IP addresses
+* run the primary by following the guide in <<Running>>
+* run the secondaries by running the command specified in <<Running>> with a parameter pointing to corresponding secondary image.
+For example,
+
+`../meta-updater/scripts/run-qemu-ota --no-gui --secondary-network secondary-images/secondary-image-qemux86-64.ota-ext4-001`
+
+`../meta-updater/scripts/run-qemu-ota --no-gui --secondary-network secondary-images/secondary-image-qemux86-64.ota-ext4-002`
+
 === Specifics of bitbaking for Raspberry Pi
 
 It is assumed that a reader is a familiar with bitbaking for Raspberry Pi in general, see link:https://docs.ota.here.com/quickstarts/raspberry-pi.html[Build a Raspberry Pi image].

docs/posix-secondaries.adoc

@@ -1,4 +1,4 @@
-= Posix Secondaries aka IP Secondaries
+= Posix Secondaries aka IP Secondaries: configuration and emulation of Primary and Secondary on a local host
 
 The goal of this doc is to guide a reader on configuring and running two executables that can be built out of the given repository source code and act as Primary and Secondary correspondingly.
 
@@ -45,7 +45,11 @@ The Primary executable is built by default, thus following build instructions ou
 
 A default configuration of aktualizr acting as Primary can be found in link:../config/sota-local-with-secondaries.toml[<src-root>/config/sota-local-with-secondaries.toml].
 
-One configuration parameter that is worth mentioning is `[uptane]: secondary_config_file` which specifies a path to secondary(ies) configuration file containing input parameters for aktualizr/Primary to communicate with any secondaries. This is a link:../config/posix-secondary-config.json[default secondary configuration for Primary]. In order to use the given default config file, either copy it into your current working directory or update `[uptane]: secondary_config_file` value so it defines a full path to the secondary config file (e.g. ``<src-root>/config/posix-secondary-config.json``).
+One configuration parameter that is worth mentioning is `[uptane]: secondary_config_file` which specifies a path
+to secondary(ies) configuration file containing input parameters for aktualizr/Primary to communicate with any secondaries.
+This is a link:../config/posix-secondary-config.json[default secondary configuration for Primary].
+In order to use the given default config file, either copy it into your current working directory or update
+`[uptane]: secondary_config_file` value so it defines a full path to the secondary config file (e.g. ``<src-root>/config/posix-secondary-config.json``).
 
 Configuration parameters of secondaries for Primary/aktualizr that are worth mentioning are:
 
@@ -84,3 +88,22 @@ $AKT_SECNDR -c $AKT_PROJ_HOME/config/posix-secondary.toml
 ....
 * Add --loglevel 0 to the aforementioned launch commands if you would like to see more logs
 * To re-register your emulated multi-ECU device (or start playing it from scratch) remove ``storage`` directory from `PRIMARY_HOME_DIR`
+
+=== Multiple secondaries
+
+In order to emulate a device containing one primary ECU along with more than one secondary ECUs the following should be done.
+
+* Run the secondary executable `<build-dir>/src/aktualizr_secondary/aktualizr-secondary` desired number of times each from different directories.
+Prior to running secondary executables, please,
+
+ ** copy the configuration file <src-root>/config/posix-secondary.toml to each directory  the secondary will be launched from.
+ Let's call such directory as `SECONDARY_HOME_DIR`;
+
+ ** update a value of `[network]:port` parameter of the config file in each `SECONDARY_HOME_DIR` directory in such way
+  that each secondary config specifies different port number (9050 by default) hence each secondary will listen on different port;
+
+* Update posix-secondary-config.json located in `PRIMARY_HOME_DIR` (see instructions in p. `Primary`) with details of each secondary
+ that was executed in previous step, specifically, add corresponding values to "secondaries" list field (e.g. `"secondaries": [{"addr": "127.0.0.1:9050"}, {"addr": "127.0.0.1:9051"}]`).
+ Once posix-secondary-config.json is updated run the primary, as result you should see that it is connected with multiple secondaries
+ in aktualizr logs as well as on UI.
+