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InfluxDB
Power Real-Time Data Analytics at Scale. Get real-time insights from all types of time series data with InfluxDB. Ingest, query, and analyze billions of data points in real-time with unbounded cardinality.
As for being able to run your own instance of things in isolation, that really depends on the fidelity you want. Firebase has an emulator you could use, and Cloud Functions/AppEngine can be built into docker images locally using the public buildpacks (but won't have the full suite of attached services), but I'd probably recommend good service mocks/stubs/fakes your services plus a pipeline that spins up a full project with Terraform, runs integration tests, then tears it down for e2e testing.
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