Doc update to configure upstream proxy to fetch modules from a Go mod… (#1146)

* Doc update to configure upstream proxy to fetch modules from a Go modules repository

* review suggestions

config.dev.toml

@@ -42,6 +42,11 @@ CloudRuntime = "none"
 
 # The filename for the include exclude filter.
 # Env override: ATHENS_FILTER_FILE
+#
+# To point Athens to an upstream proxy to fetch modules,
+# set GlobalEndpoint to "https://<url_to_upstream>"
+# and also ensure that FilterFile is  set to a fully qualified file name 
+# that contains the letter `D` (for "Direct Access") in the first line.
 FilterFile = ""
 
 # Timeout is the timeout for external network calls in seconds
@@ -70,6 +75,11 @@ Port = ":3000"
 # The endpoint for a package registry in case of a proxy cache miss
 # NOTE: Currently no registries have been implemented
 # Env override: ATHENS_GLOBAL_ENDPOINT
+#
+# To point Athens to an upstream proxy to fetch modules,
+# set GlobalEndpoint to "https://<url_to_upstream>"
+# and also ensure that FilterFile is  set to a fully qualified file name 
+# that contains the letter `D` (for "Direct Access") in the first line.
 GlobalEndpoint = "http://localhost:3001"
 
 # BASIC AUTH OPTIONS 

docs/content/configuration/_index.md

@@ -16,3 +16,9 @@ There are numerous version control systems available to us as developers.  In th
 In Athens we support many storage options. In this section we'll describe how they can be configured
 
  - [Storage](/configuration/storage)
+
+
+ ### Upstream proxy
+ In this section we'll describe how the upstream proxy can be configured to fetch all modules from a Go Modules Repository such as [GoCenter](https://gocenter.io) or another Athens Server.
+
+  - [Upstream](/configuration/upstream)

docs/content/configuration/upstream.md

@@ -0,0 +1,28 @@
+---
+title: Configuring Upstream Proxy to use an Upstream Go Modules Repository
+description: How to Configure Athens to Fetch Missing Modules From an Upstream Module Repository Like GoCenter, or Another Athens Server
+weight: 1
+---
+
+By default, Athens fetches module code from an upstream VCS like github.com, but this can be configured to use a Go modules repository like GoCenter or another Athens Server.
+
+1. Create a filter file (e.g ```/usr/local/lib/FilterForGoCenter```) with letter `D` (stands for "direct access") in first line. For more details, please refer to documentation on  - [Filtering Modules](/configuration/filter)
+
+    ```
+    # FilterFile for fetching modules directly from upstream
+    D
+    ```
+1. If you are not using a config file, create a new config file (based on the sample config.dev.toml) and edit values to match your environment).
+Additionally in the current or new config file, set the following parameters as suggested:
+
+    ```
+    FilterFile = "/usr/local/lib/FilterForGoCenter"
+    GlobalEndpoint = "https://<url_to_uptream>"
+    # To use GoCenter for example, replace <url_to_upstream> with gocenter.io
+    ```
+1. Restart Athens specifying the updated current or new config file.
+
+    ```
+    /proxy  -config_file <path-to updated  current or new configfile>
+    ```
+1. Verify the new configuration using the steps mentioned in ("Try out Athens" document)[/try-out], and go through the same walkthrough example.