Deriving device connection string from the environment - azure-iot-edge

Question

IoT modules can be created from the environment using :
ModuleClient.CreateFromEnvironmentAsync(settings)
However, there does not seem to be an equivalent method for devices. For now, I am setting the device connection string in the program to test it out, but is there a better way to read teh connection string from iotedge/config.yaml for all the edge devices deployed out there?
Methods to do so for .NET and python would be appreciated.

Answer 1

You can use a yaml parse library to deserialize the document, such as YamlDotNet. In fact, you can refer to YamlDocument in iot edge. But in the class, it does not provide a method to get the key value. Please refer to following code.
public class YamlDocument
{
readonly Dictionary<object, object> root;
public YamlDocument(string input)
{
var reader = new StringReader(input);
var deserializer = new Deserializer();
this.root = (Dictionary<object, object>)deserializer.Deserialize(reader);
}
public object GetKeyValue(string key)
{
if(this.root.ContainsKey(key))
{
return this.root[key];
}
foreach(var item in this.root)
{
var subItem = item.Value as Dictionary<object, object>;
if(subItem != null && subItem.ContainsKey(key))
{
return subItem[key];
}
}
return null;
}
}
And then you can get the device connection string from the config.yaml. If you use python, you can import yaml library to analysis the file.
StreamReader sr = new StreamReader(#"C:\ProgramData\iotedge\config.yaml");
var yamlString = sr.ReadToEnd();
var yamlDoc = new YamlDocument(yamlString);
var connectionString = yamlDoc.GetKeyValue("device_connection_string");
Console.WriteLine("{0}", connectionString);

Answer 2

To get the config file from the host, add the following to the docker deployment file. Note that the source file is config1.yaml which is the same as config.yaml except that it has read permissions for everyone not just root.
"createOptions": "{\"HostConfig\":{\"Binds\":[\"/etc/iotedge/config1.yaml:/app/copiedConfig.yaml\"]}}"
With the above line in place, the copiedConfig.yaml file can be used in the container, along with #Michael Xu's parsing code to derive teh connection string.
Long term, one may want to use the device provisioning service anyway but hope this helps for folks using device conenction strings for whatever reason..