promoting comment to part of readme

Author: sjanssen2

README.md

@@ -16,3 +16,32 @@ Also, if Qiita is running with the default server SSL certificate, you need to e
 
 export QIITA_ROOT_CA=<QIITA_INSTALL_PATH>/qiita_core/support_files/ci_rootca.crt
 ```
+
+Configure for cloud computing
+-----------------------------
+In the default scenario, Qiita main and Qiita plugins are executed on the same
+machines, maybe spread across a Slurm or other grid compute cluster, but main
+and plugins have direct access to all files in `BASE_DATA_DIR`.
+
+This can be different, if you set up Qiita within a cloud compute environment,
+where main and plugins do **not** share one file system. In this case, input-
+files must first be transferred from main to plugin, then plugin can do its
+processing and resulting files must be transferred back to main, once
+processing is finished. To achieve this, the qiita_client, as it is part of
+each plugin, provides the two functions for this file transfer
+`fetch_file_from_central` and `push_file_to_central`. According to
+`self._plugincoupling`, these functions operate on different "protocols";
+as of 2025-08-29, either "filesystem" or "https". Switch to **"https"** for
+cloud environments, default is **filesystem**.
+
+The plugin coupling protocoll can be set in three ways
+
+    1. default is always "filesystem", i.e. _DEFAULT_PLUGIN_COUPLINGS
+        This is to be downward compatible.
+    2. the plugin configuration can hold a section 'network' with an
+        option 'PLUGINCOUPLING'. For old config files, this might not
+        (yet) be the case. Therefore, we are double checking existance
+        of this section and parameter here.
+    3. you can set the environment variable QIITA_PLUGINCOUPLING
+        Precedence is 3, 2, 1, i.e. the environment variable overrides the
+        other two ways.

qiita_client/plugin.py

@@ -282,16 +282,6 @@ def __call__(self, server_url, job_id, output_dir):
         with open(self.conf_fp, 'U') as conf_file:
             config.readfp(conf_file)
 
-        # the plugin coupling protocoll can be set in three ways
-        # 1. default is always "filesystem", i.e. _DEFAULT_PLUGIN_COUPLINGS
-        #    This is to be downward compatible.
-        # 2. the plugin configuration can hold a section 'network' with an
-        #    option 'PLUGINCOUPLING'. For old config files, this might not
-        #    (yet) be the case. Therefore, we are double checking existance
-        #    of this section and parameter here.
-        # 3. you can set the environment variable QIITA_PLUGINCOUPLING
-        # Precedence is 3, 2, 1, i.e. the environment variable overrides the
-        # other two ways.
         plugincoupling = self._DEFAULT_PLUGIN_COUPLINGS
         if config.has_section('network') and \
            config.has_option('network', 'PLUGINCOUPLING'):

qiita_client/qiita_client.py

@@ -773,7 +773,7 @@ def fetch_file_from_central(self, filepath, prefix=None):
         str : the filepath of the requested file within the local file system
         """
         target_filepath = filepath
-        if (prefix is not None) and (prefix != ""):
+        if not prefix:
             # strip off root
             if filepath.startswith(os.path.abspath(os.sep)):
                 target_filepath = target_filepath[
@@ -782,7 +782,7 @@ def fetch_file_from_central(self, filepath, prefix=None):
             target_filepath = os.path.join(prefix, target_filepath)
 
         if self._plugincoupling == 'filesystem':
-            if prefix != '':
+            if not prefix:
                 # create necessary directory locally
                 os.makedirs(os.path.dirname(target_filepath), exist_ok=True)