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An enterprise-grade Java-based, Apache 2.0 licensed Ethereum client https://wiki.hyperledger.org/display/besu
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101 lines
4.3 KiB
101 lines
4.3 KiB
description: Pantheon high availability
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# High Availability
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To enable high availability to the [RPC Pub/Sub API over WebSockets](../Pantheon-API/RPC-PubSub.md)
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or the [JSON-RPC API](../Pantheon-API/Using-JSON-RPC-API.md) run and synchronize multiple Pantheon
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nodes to the network. Use a load balancer to distribute requests across nodes in the cluster that
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are ready to receive requests.
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## Determining When a Node is Ready
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Use the [readiness endpoint](../Pantheon-API/Using-JSON-RPC-API.md#readiness-and-liveness-endpoints)
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to determine when a node is ready.
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!!! note
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The minimum number of peers and number of blocks from the best known block for a node to be considered ready
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is deployment specific.
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## Transaction Nonces
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The account nonce for the next transaction is obtained using [`eth_getTransactionCount`](../Reference/Pantheon-API-Methods.md#eth_gettransactioncount).
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The account nonce depends on the transactions in the [transaction pool](../Using-Pantheon/Transactions/Transaction-Pool.md).
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If [`eth_getTransactionCount`](../Reference/Pantheon-API-Methods.md#eth_gettransactioncount) and
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[`eth_sendRawTransaction`](../Reference/Pantheon-API-Methods.md#eth_sendrawtransaction) requests for a specific account
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are sent to multiple nodes, the [`eth_getTransactionCount`](../Reference/Pantheon-API-Methods.md#eth_gettransactioncount)
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results can be incorrect.
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!!! note
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If using [private transactions](../Privacy/Privacy-Overview.md), `eea_getTransactionCount` is used to obtain
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the account nonce and [`eea_sendRawTransaction`](../Reference/Pantheon-API-Methods.md#eea_sendrawtransaction)
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to send private transactions.
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To get correct account nonces when distributing requests across a cluster, do one of:
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* Track the next nonce outside of the Pantheon node (as MetaMask does)
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* Configure the load balancer in sticky mode so requests from a specific account are sent to a single
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node unless that node is unavailable.
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## Subscriptions
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You can subscribe to events using:
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* [RPC Pub/Sub over WebSockets](../Pantheon-API/RPC-PubSub.md)
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* [Filters over HTTP](../Using-Pantheon/Accessing-Logs-Using-JSON-RPC.md)
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We recommend using [RPC Pub/Sub over WebSockets](../Pantheon-API/RPC-PubSub.md) because WebSockets
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connections are associated a specific node and do not require using the load balancer in sticky mode.
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If using [filters over HTTP](../Using-Pantheon/Accessing-Logs-Using-JSON-RPC.md), configure the load balancer
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in sticky mode to associate the subscription with a specific node.
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## Recovering from Dropped Subscriptions
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Subscriptions can be dropped if:
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* WebSockets connection is disconnected
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* Node serving the subscription is removed from the ready pool
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If a subscription is dropped, events can be missed while reconnecting to a different node.
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To recover dropped messages, create another subscription and follow the process for that [subscription type](../Pantheon-API/RPC-PubSub.md#subscribing):
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* [`newHeads`](#new-headers)
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* [`logs`](#logs)
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* [`newPendingTransactions`](#new-pending-transactions)
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* [`droppedPendingTransactions`](#dropped-pending-transactions)
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* [`syncing`](#syncing)
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### New Headers
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Use [`eth_getBlockByNumber`](../Reference/Pantheon-API-Methods.md#eth_getblockbynumber) to request information on
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blocks from the last block before the subscription dropped to the first block received from the new subscription.
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### Logs
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Use [`eth_getLogs`](../Reference/Pantheon-API-Methods.md#eth_getlogs) to request logs from the block number
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of the last log received before the subscription dropped to the current chain head.
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### New Pending Transactions
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Use [`txpool_pantheonTransactions`](../Reference/Pantheon-API-Methods.md#txpool_pantheontransactions) to
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request all pending transactions for the new node.
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!!! note
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Nodes do not all store the same pending transactions.
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### Dropped Pending Transactions
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Use [`txpool_pantheonTransactions`](../Reference/Pantheon-API-Methods.md#txpool_pantheontransactions) to
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request all pending transactions for the new node.
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!!! note
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Nodes do not all store the same pending transactions.
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### Syncing
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The syncing state of each node is specific to that node. Use [`eth_syncing`](../Reference/Pantheon-API-Methods.md#eth_syncing)
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to retrieve the syncing state of the new node.
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