blockscout/docs/env-variables.md

# BlockScout Env Variables

Below is a table outlining the environment variables utilized by BlockScout.

**Notes:**
- This table is horizontally scrollable, version information is located in the last column.
- Settings related to the `ETHEREUM_JSONRPC_VARIANT` variable and client related settings for running a full archive node with geth or parity are located in [this forum post](https://forum.poa.network/t/faq-what-settings-are-required-on-a-parity-or-geth-client/1805).
- Additional information related to certain variables is available on the [ansible deployment](ansible-deployment.md) page.
- To set variables using the CLI, use the export command. For example: 
```bash
$ export ETHEREUM_JSONRPC_VARIANT=parity
$ export COIN=POA
$ export NETWORK=POA
```


| Variable | Required | Description | Default | Version |
| --- | --- | --- | ---| --- |
| `NETWORK`| :white_check_mark:  | Environment variable for the main EVM network such as Ethereum Network or POA Network | POA Network | all |
| `SUBNETWORK` | :white_check_mark: | Environment variable for the subnetwork such as Core or Sokol Network | Sokol Testnet | all |
| `NETWORK_ICON` | :white_check_mark: | Environment variable for the main network icon or testnet icon. Two options are  `_test_network_icon.html` and `_network_icon.html` | `_test_network_icon.html` | all |
| `LOGO` | :white_check_mark: | Environment variable for the logo image location. The logo files names for different chains can be found [here](https://github.com/poanetwork/blockscout/tree/master/apps/block_scout_web/assets/static/images) | /images/blockscout_logo.svg | all |
| `ETHEREUM_JSONRPC_VARIANT` | :white_check_mark: | This environment variable is used to tell the application which RPC Client the node is using (i.e. Geth, Parity, or Ganache) | parity | all |
| `ETHEREUM_JSONRPC_HTTP_URL` | :white_check_mark: | The RPC endpoint used to fetch blocks, transactions, receipts, tokens. | localhost:8545 | all |
| `ETHEREUM_JSONRPC_TRACE_URL` | | The RPC endpoint specifically for the Geth/Parity client used by trace_block and trace_replayTransaction. This can be used to designate a tracing node. | localhost:8545 | all |
| `ETHEREUM_JSONRPC_WS_URL` | :white_check_mark: | The WebSockets RPC endpoint used to subscribe to the `newHeads` subscription alerting the indexer to fetch new blocks. | ws://localhost:8546 | all |
| `NETWORK_PATH` | | Used to set a network path other than what is displayed in the root directory. An example would be to add /eth/mainnet/ to the root directory. | (empty) | all |
| `SECRET_KEY_BASE` | :white_check_mark: | Use mix phx.gen.secret to generate a new Secret Key Base string to protect production assets. | (empty) | all |
| `CHECK_ORIGIN` | | Used to check the origin of requests when the origin header is present. It defaults to false. In case of true, it will check against the host value. | false | all |
| `PORT` | :white_check_mark: | Default port the application runs on is 4000 | 4000 | all |
| `COIN` | :white_check_mark: | The coin here is checked via the Coinmarketcap API to obtain USD prices on graphs and other areas of the UI | POA | all |
| `METADATA_CONTRACT` | | This environment variable is specifically used by POA Network to obtain Validators information to display in the UI. | (empty) | all |
| `VALIDATORS_CONTRACT` | | This environment variable is specifically used by POA Network to obtain the Emission Fund contract. | (empty) | all |
| `SUPPLY_MODULE` | | This environment variable is used by the xDai Chain in order to tell the application how to calculate the total supply of the chain. | false | all |
| `SOURCE_MODULE` | | This environment variable is used to calculate the exchange rate and is specifically used by the xDai Chain. | false | all |
| `DATABASE_URL` | | Production environment variable to define the Database endpoint. | (empty) | all |
| `POOL_SIZE` | | Production environment variable to define the number of database connections allowed. | 20 | all |
|  `ECTO_USE_SSL`| | Production environment variable to use SSL on Ecto queries. | true | all |
|  `DATADOG_HOST` | | Host configuration setting for [Datadog integration](https://docs.datadoghq.com/integrations/) | (empty) | all |
|  `DATADOG_PORT` | | Port configuration setting for [Datadog integration](https://docs.datadoghq.com/integrations/). | (empty} | all |
| `SPANDEX_BATCH_SIZE` | | [Spandex](https://github.com/spandex-project/spandex) and Datadog configuration setting. | (empty) | all |
|  `SPANDEX_SYNC_THRESHOLD` | | [Spandex](https://github.com/spandex-project/spandex) and Datadog configuration setting.  | (empty) | all |
| `HEART_BEAT_TIMEOUT` | | Production environment variable to restart the application in the event of a crash. | 30 | all |
| `HEART_COMMAND` | | Production environment variable to restart the application in the event of a crash. | systemctl restart explorer.service | all |
| `BLOCKSCOUT_VERSION` | | Added to the footer to signify the current BlockScout version. | (empty) | v1.3.4+ |
| `RELEASE_LINK` | | The link to Blockscout release notes in the footer. | <u>https: //github.com/poanetwork/</u> <br /><u>blockscout/releases/</u> <br /> <u>tag/${BLOCKSCOUT_VERSION}</u> | v1.3.5+ |
| `ELIXIR_VERSION` | | Elixir version to install on the node before Blockscout deploy. | (empty) | all |
| `BLOCK_TRANSFORMER` | | Transformer for blocks: base or clique. | base |  v1.3.4+ |
| `GRAPHIQL _TRANSACTION` | | Default transaction in query to GraphiQL. | (empty) |  v1.3.4+ |
| `FIRST_BLOCK` | | The block number, where indexing begins from. | 0 |  v1.3.8+ |
| `LAST_BLOCK` | | The block number, where indexing stops. | (empty) | master |
| `TXS_COUNT_CACHE_PERIOD` | | Interval in seconds to restart the task, which calculates the total txs count. | 60 * 60 * 2 |  v1.3.9+ |
| `ADDRESS_WITH_BALANCES` <br /> `_UPDATE_INTERVAL`|  | Interval in seconds to restart the task, which calculates addresses with balances. | 30 * 60 |  v1.3.9+ |
| `LINK_TO_OTHER_EXPLORERS` | | true/false. If true, links to other explorers are added in the footer  | (empty)  |  v1.3.0+ |
| `COINMARKETCAP_PAGES` | | the number of pages on coinmarketcap to list in order to find token's price  | 10 |  v1.3.10+ |
| `SUPPORTED_CHAINS` | | Array of supported chains that displays in the footer and in the chains dropdown. This var was introduced in this PR [#1900](https://github.com/poanetwork/blockscout/pull/1900) and looks like an array of JSON objects.  | (empty) |  v2.0.0+ |
| `BLOCK_COUNT_CACHE_PERIOD ` | | time to live of cache in seconds. This var was introduced in [#1876](https://github.com/poanetwork/blockscout/pull/1876)  | 600 |  v2.0.0+ |
| `ALLOWED_EVM_VERSIONS ` | | the comma-separated list of allowed EVM versions for contracts verification. This var was introduced in [#1964](https://github.com/poanetwork/blockscout/pull/1964)  | "homestead, tangerineWhistle, spuriousDragon, byzantium, constantinople, petersburg" |  v2.0.0+ |
| `DISABLE_WEBAPP` | | If `true`, endpoints to webapp are hidden (compile-time) | `false` | master |
| `DISABLE_READ_API` | | If `true`, read-only endpoints to API are hidden (compile-time) | `false` | master |
| `DISABLE_WRITE_API` | | If `true`, write endpoints to API are hidden (compile-time) | `false` | master |
| `DISABLE_INDEXER` | | If `true`, indexer application doesn't run | `false` | master |
| `WEBAPP_URL` | | Link to web application instance, e.g. `http://host/path` | (empty) | master |
| `API_URL` | | Link to API instance, e.g. `http://host/path` | (empty) | master |