update README

Author: LuiggiTenorioK

docker/README.md

@@ -2,13 +2,21 @@
 
 To build the image you can execute `./build.sh`, or:
 
+```bash
+docker build -t autosubmit-gui
+```
+
+> **NOTE**: The default image builds a GUI which `AUTOSUBMIT_API_SOURCE` is the relative path `/api`. This is needed if you want to change it using environment variables when starting the container.
+
+On the build, you can fix a API URL by doing:
+
 ```bash
 docker build \
-    --build-arg "AUTOSUBMIT_API_SOURCE=http://127.0.0.1:8000" \ # Required argument
+    --build-arg "AUTOSUBMIT_API_SOURCE=http://127.0.0.1:8000" \
     -t autosubmit-gui
 ```
 
-On the build, you can select a different tag/branch/commit by running:
+Also, you can select a different tag/branch/commit by running:
 
 ```bash
 docker build \
@@ -17,7 +25,9 @@ docker build \
     -t autosubmit-gui
 ```
 
-Other `--build-arg` are available that are related to the build environment variables with prefix `REACT_APP_`. See the `Dockerfile` to know more about it. **Note: This environment variables are only used while building, modifying them on runtime will not make any change.**
+Other `--build-arg` are available that are related to the build environment variables with prefix `REACT_APP_`. See the `Dockerfile` to know more about it. 
+
+> **IMPORTANT: This environment variables that are set using the build arguments are only used while building, modifying them on runtime will not make any change.**
 
 ## Run
 
@@ -29,4 +39,19 @@ docker run --name autosubmit-gui-container \
     autosubmit-gui
 ```
 
-**Remember to map the port `8080` to the one you desire. In the example above, it is mapped to port `8089`.**
+**Remember to map the port `8080` to the one you desire. In the example above, it is mapped to port `8089`.**
+
+If the `AUTOSUBMIT_API_SOURCE` was not set during the build, the GUI will use the relative path `/api`. This means, if the GUI is served in `localhost:8080`, it will send the API requests to `localhost:8080/api`.
+
+This mechanism works because the container can proxy the requests sent to `localhost:8080/api` to another URL using Nginx. And this can be set doing:
+
+```bash
+docker run --name autosubmit-gui-container \
+    --rm -d -p 8080:8080 \
+    -e "API_URL_PROXY=https://hostname/external-as-api/" \
+    autosubmit-gui
+```
+
+This will forward the requests send to `localhost:8080/api` to `https://hostname/external-as-api/`. For example, `GET localhost:8080/api/v4/experiments` will go to `GET https://hostname/external-as-api/v4/experiments`.
+
+With this option there is no need to build the image again.

docker/build.sh

@@ -1,5 +1,3 @@
 #!/bin/bash
 
-docker build \
-    --build-arg "AUTOSUBMIT_API_SOURCE=http://127.0.0.1:8000" \
-    -t autosubmit-gui --progress=plain . &> build.log
+docker build -t autosubmit-gui --progress=plain . &> build.log