Improves documentation

 * Describes better available source tree sharing method (between
xds-agent and xds-server), and which to prefer depending on the
deployment setup.
 * Gives indication about how to pass RSYNC_TARGET and RSYNC_PREFIX
 env vars to the helloworld-native-application build process.
 * Swap chapter order (build before config)

Change-Id: Ie4c22f277a59b0405744d71b0fadff67c5d5d025
Signed-off-by: Johann CAHIER <johann.cahier@iot.bzh>

1 files changed, 47 insertions, 0 deletions

diff --git a/docs/part-2/2_xds-agent/2_config.md b/docs/part-2/2_xds-agent/2_config.md
new file mode 100644
index 0000000..9e912cb
--- /dev/null
+++ b/docs/part-2/2_xds-agent/2_config.md
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+# Configuration
+
+xds-agent configuration is driven by a JSON config file.
+
+The tarball mentioned in previous section includes this file with default settings.
+
+Here is the logic to determine which conf file will be used:
+
+1. from command line option: `--config myConfig.json`
+1. `$HOME/.xds/agent/agent-config.json` file
+1. `/etc/xds/agent/agent-config.json` file
+
+Supported fields in configuration file are (all fields are optional and example
+below corresponds to the default values):
+
+- **httpPort** : http port of agent REST interface
+- **webAppDir** : location of client webapp / dashboard (default: webapp/dist)
+- **logsDir**  : directory to store logs (eg. syncthing output)
+- **xdsServers** : an array of xds-server object
+  - **xdsServers.url**: url of xds-server to connect to
+- **syncthing**: a object defining syncthing settings
+  - **syncthing.binDir** : syncthing binaries directory (default: executable directory)
+  - **syncthing.home"** : syncthing home directory (usually .../syncthing-config)
+  - **syncthing.gui-address** : syncthing gui url (default <http://localhost:8386>)
+  - **syncthing.gui-apikey** : syncthing api-key to use (default auto-generated)
+
+```json
+{
+    "httpPort": "8800",
+    "webAppDir": "./www",
+    "logsDir": "${HOME}/.xds/agent/logs",
+    "xdsServers": [
+        {
+          "url": "http://localhost:8000"
+        }
+    ],
+    "syncthing": {
+        "home": "${HOME}/.xds/agent/syncthing-config",
+        "gui-address": "http://localhost:8386",
+        "gui-apikey": "1234abcezam"
+    }
+}
+```
+
+>**Note:**
+>
+>environment variables are supported by using `${MY_VAR}` syntax.