## Umbrella Project Organization BlockScout is an Elixir [umbrella project](https://elixir-lang.org/getting-started/mix-otp/dependencies-and-umbrella-projects.html). Each directory under `apps/` is a separate [Mix](https://hexdocs.pm/mix/Mix.html) project and [OTP application](https://hexdocs.pm/elixir/Application.html), but the projects can use each other as a dependency in their `mix.exs`. Each OTP application has a restricted domain. | Directory | OTP Application | Namespace | Purpose | |:------------------------|:--------------------|:------------------|:--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------| | `apps/ethereum_jsonrpc` | `:ethereum_jsonrpc` | `EthereumJSONRPC` | Ethereum JSONRPC client. It is allowed to know `Explorer`'s param format, but it cannot directly depend on `:explorer` | | `apps/explorer` | `:explorer` | `Explorer` | Storage for the indexed chain. Can read and write to the backing storage. MUST be able to boot in a read-only mode when run independently from `:indexer`, so cannot depend on `:indexer` as that would start `:indexer` indexing. | | `apps/block_scout_web` | `:block_scout_web` | `BlockScoutWeb` | Phoenix interface to `:explorer`. The minimum interface to allow web access should go in `:block_scout_web`. Any business rules or interface not tied directly to `Phoenix` or `Plug` should go in `:explorer`. MUST be able to boot in a read-only mode when run independently from `:indexer`, so cannot depend on `:indexer` as that would start `:indexer` indexing. | | `apps/indexer` | `:indexer` | `Indexer` | Uses `:ethereum_jsonrpc` to index chain and batch import data into `:explorer`. Any process, `Task`, or `GenServer` that automatically reads from the chain and writes to `:explorer` should be in `:indexer`. This restricts automatic writes to `:indexer` and read-only mode can be achieved by not running `:indexer`. |