yashjain28/google-pub-sub

this library support pull subscription to Google IoT Core topics using an existing subscription

ipm package: google-pub-sub

Overview

This package is a template system to connect with Google Cloud using REST subscribe to topics. It uses the Pull Subscription approach for subscription.

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Setup

Gcloud Setup Summary
Create Gcloud account
Create a project in gcloud
Create a topic(optional)
Create a subscription for the desired topic
Create a service account

1. Setup on Gcloud Detailed: Following steps are assuming user already has an account and has access to Gcloud IoT Console.
   1. If you already have a project created and also have a topic which you wish to subscribe to, then directly go to step 3.
   2. Perform the Iot core quickstart: This will involve creating a device, device registry & a certificate, creating a topic and a subscription.
   3. Now that you have a topic in a project to subscribe to, create a pull subscription if you don't already have one. Follow this link to create a pull subscription.
   4. We use a service account to perform the pull subscription over HTTP REST. Follow the steps here to create a service account on google and generate a key. This key is used to generate access token that is used to perform the pull and acknowledgement. Things to note here are:
      1. default maximum validity for access token is 3600 seconds.
      2. The additional steps to increase the default maximum validity for access token are here
2. Setup on ClearBlade:
   1. Get the Desired Credentials and update the Google IoT Configuration Library. The credentials include PROJECT_ID, MAX_MESSAGES_TO_PULL, SUBSCRIPTION_NAME, SUBSCRIPTION_SERVICE_ACCOUNT_PRIVATE_KEY from the above Gcloud checklist summary.
   2. Restart the pullSubscription service once the GoogleIoTConfig Library is updated.
   3. Update the pullTimer and updateAccessTokenTimer based on your use-case.

Usage

The accessTokenManager service listens on a timer to fetch a new access token. The reason we do that is the expiry time of an access token is limited, a maximum of 3600s. This service updates the AccessToken in a shared cache, which is used by the pullSubscription service to make a pull to the subscription.

Note: One can manually update the access token in the shared cache, by simply invoking the accessTokenManager service.

Assets

Code Services

• accessTokenManager -- a service that uses the private for a service account along with other credentials in the GoogleIoTConfig library to gain the access token and update the shared cache with the latest access_token. This service runs of a timer, updateAccessTokenTimer. The frequency of execution of this timer should be less than 3600s, since the access_token has a maximum expiry time of 3600s.
• pullSubscription -- a stream service which regularly pulls on a topic. The determine of pull's is defined by the pullTimer. If the pullTimer fires every 20 seconds, then the service makes a pull to the topic on google every 20 seconds. It reads the accessToken from the shared cache which is updated regularly by the accessTokenManager service.

Code Libraries

GoogleIoTConfig -- a configuration library, which holds constants specific to Google IoT.

Timers

The timers can be updated based on your use-case:

• pullTimer - this timer defines the frequency of your pull.
• updateAccessTokenTimer - this timer defines the frequency at which the access token gets updated.

Shared Cache

AccessTokenCache - this cache stores the latest and active access_token. The expiry time for this cache is set to 3600s.