POC MongoDB - CosmoDB with Mongo API

Compatibility tests when switching from MongoDB to CosmoDB with Mongo API

Why MongoDB 3.6?

We are using MongoDB 3.6 beacuse its one of the version where LTS expiry is still to be defined: https://www.mongodb.com/support-policy

• MongoDB 3.4 has LTS till 1 Jan 2020.
• MongoDB 3.2 LTS expired on 2019.

Getting Started

git clone https://github.com/conplementAG/mongodb-cosmosdb-compatibility

Prerequisites

• Docker
• Docker Compose (Included in Docker Desktop)

Installing

Azure CosmoDB

First you need to create a CosmoDB instance in Azure.

If you are not logged in Azure use az login from the cli.

Be sure to set the right subscription using az account set --subscription xxxxxxxxx.

Now you can change the parameter and run the script set-cosmosdb.sh that sits on the scripts folder.

This will create cosmodb instance and output the neccessary information that you will need to follow along.

Note: Aggregation pipelines by default are disabled. The set-cosmosdb.sh enables them but if you create the CosmoDB manually go to the CosmoDB account under Preview Features and enable Aggregation Pipeline.

Azure CosmoDB Emulator for local development

Download and install CosmoDB emulator from https://aka.ms/cosmosdb-emulator.

If you want to use docker for running the cosmodb emulator you will need to enable windows containers, currently it dosent run on Linux Containers.

For our use case we will install the emulator on the host machine.

By default CosmoDB emulator starts only the SQL endpoint enabled so you need to enable the MongoDB endpoint manually.

• https://docs.microsoft.com/en-us/azure/cosmos-db/local-emulator-release-notes#release-notes

To enable MongoDB endpoint start the emulator from CMD with Administrative rights using the option /EnableMongoDbEndpoint

E.g. C:\Programs\Azure Cosmos DB Emulator /EnableMongoDbEndpoint.

Build docker image

From the root folder build the Docker Image docker build . -t poc:latest

Start it with docker-compose

Docker compose will spin up three containers for our application + the mongo db instance.

Each of our app containers will need their .env files namely:

• app.cosmos.env used to hold the credentials of the cosmos db instance in azure
• app.localcosmos.env used to hold the credentials of the local cosmos db instnace
• app.mongo.env used to hold the credentials of the local mongodb instance
• mongo.env contains the init username and password configuration, template is mongo.env.template

After creating and filling the env files from the root folder you can start everything using docker-compose up

Known issues

Container to host accessing services

When installing the azure cosmos emulator in the host machine the url to access the locahost from the container is host.docker.internal which points to the ip address of the host machine.

One alternative is to run the container which accesses the emulator using network_mode=host but be aware that Docker Desktop for Mac and Windows dosent support it. It works only on Linux.

That means in the app.localcosmos.env file the DB_CONNSTR contains the value mongodb://host.docker.internal:10255/dbName?ssl=true to reference the host machine.

Volume mapping for development mode

If you mount the ./src folder into the container so that while the container is running you can change the code be sure that from your host machine you didnt install nodes_modules first. Some of the modules when installed for Windows will download command scripts that wont work in Linux.

If you install the node_modules from the container then it will work when you change the code locally (but not when run also locally).

Testing

If you want to test each of the connections you can log into the respective containers using docker exec -it xxxcontainer_idxxx "/bin/bash"

The application has been configured with script commands which can be run using npm run command_name

• test runs all the tests once (Default)
• twatch runs the tests on watch mode, helpful when mounting the .\src folder and connection to the container interactivly.
• test:debug opens the possibility to debug the tests remotly using chrome://inspect (dont forget to port map in the docker-compose.yaml)
• start which starts nodemon index.js. Use it to keep the container alive (e.g. to connect to the container). You can override it in docker-compose file. The tests are written to test basic CRUD operations, Aggregations and more complex Queuries.