Share data directly between ESPHome nodes

In certain special cases it might be desired to avoid placing any middleware like an MQTT or a home automation server just to transfer small bits of data from one node to another. Direct data polling is possible using HTTP, but beware that the involved components are resource hungry and may be less stable on long term. The webserver embedded in the node is not designed to constantly serve a large amount of requests.

The primary node holding the data we need to retrieve from will be the server, and the others polling for it will be the clients (can be multiple).

Server part

Setting up a webserver using the Web Server Component on the primary node will make available the required sensor data through a REST API interface.

web_server:
  port: 80

Client part

On the client nodes we need an HTTP Request with an id set, and a Template Sensor to make it accessible locally.

http_request:
  useragent: esphome/device
  id: http_request_id

sensor:
  - platform: template
    name: "Template sensor on client"
    id: template_sensor_id

Pulling the data

To automate the request for data, we use an interval Component requesting the URL pointing to the sensor id for which the state is needed. See REST API on how to build up the URL for your sensors.

In the example below we request the value of a sensor from the server node, and after parsing the resulted JSON string we publish it to the local template sensor:

interval:
  - interval: 60s
    then:
      - http_request.get:
          url: http://ip or nodename.local/sensor/ID_of_the_sensor
          on_response:
            then:
              - lambda: |-
                  json::parse_json(id(http_request_id).get_string(), [](JsonObject root) {
                      id(template_sensor_id).publish_state(root["value"]);
                  });

Result

../_images/server.png

Server side real sensor

../_images/clients.png

Client side template sensor

Increasing security

For security reasons, it’s always recommended to protect the web interface of the nodes with authentication, even if you’re using them on your local network.

Server part

Add authentication to the web_server component on the primary node:

web_server:
  port: 80
  auth:
    username: !secret admin
    password: !secret web_server_password

Client part

Add an Authorization header to your http_request.get action. The simplest way to determine a working authorization header is to visit the password-protected REST URL of the primary node using a browser while watching the network traffic in the browser’s developer tools. If you look at the headers of the request sent by the browser, you’ll find the Authorization header it sends to the node, and you can copy it for your own replay:

interval:
  - interval: 60s
    then:
      - http_request.get:
          url: http://ip or nodename.local/sensor/ID_of_the_sensor
          headers:
            Authorization: 'Digest username="admin", realm="asyncesp", nonce="xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx", uri="/sensor/ID_of_the_sensor", response="xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx", opaque="xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx", qop=auth, nc=xxxxxxxx, cnonce="xxxxxxxxxxxxxxxx"'
          on_response:
            then:
              - lambda: |-
                  json::parse_json(id(http_request_id).get_string(), [](JsonObject root) {
                      id(template_sensor_id).publish_state(root["value"]);
                  });

See Also