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127 lines
6.9 KiB
127 lines
6.9 KiB
6 years ago
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---
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layout: core
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permalink: /:collection/:path.html
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---
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# Overview of the Atlas network
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{:.no_toc}
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This document describes the Atlas network, a peer-to-peer content-addressed
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storage system whose chunks' hashes are announced on a public blockchain. Atlas
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allows users and developers to **permanently store** chunks of data that are
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**replicated across every peer.** As long as at least one Atlas peer is online,
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all chunks are available to clients.
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This document is aimed at developers and technical users. The following
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concepts are discussed:
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* TOC
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{:toc}
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The reader of this document is expected to be familiar with the [Blockstack Naming Service]({{site.baseurl}}/core/naming/introduction.html)(BNS), as well as Blockstack's
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storage system [Gaia](https://github.com/blockstack/gaia). We advise the reader
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to familiarize themselves with both systems before approaching this document.
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## Architecture
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Atlas is designed to integrate with BNS in order to allow users to
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store name state off-chain, encoded as a DNS zone file.
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The overwhelmingly-common use-cases in Blockstack are:
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* Storing a name's routing information for its owners' [Gaia](https://github.com/blockstack/gaia)
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datastores.
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* Storing BNS subdomain transactions and associated state.
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Atlas is a middleware system in Blockstack. Most developers do not
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interact with it directly. BNS clients like the
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[Blockstack Browser](https://github.com/blockstack/blockstack-browser)
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automatically generate zone files for the names they register, and automatically
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propagate them to the Atlas network. BNS API endpoints, including our
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[public endpoint](https://core.blockstack.org) and the
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[blockstack.js](https://github.com/blockstack/blockstack.js) library,
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will automatically fetch zone files from Atlas when they need to look
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up data in Gaia (such as profiles and app data).
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```
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+--------------+ +---------------+ +----------------+
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clients | Blockstack | | blockstack.js | | BNS API module |
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| Browser | | | | |
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+--------------+ +---------------+ +----------------+
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^ ^ ^ ^ ^ ^
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V | V | V |
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+----------+ | +----------+ | +----------+ |
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Gaia | Gaia hub | | | Gaia hub | | | Gaia hub | |
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+----------+ | +----------+ | +----------+ |
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V V V
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+---------------------------------------------------------------+
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Atlas | Atlas Peer Network |
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+----------+------+----------+-----+----------+------+----------+
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BNS | BNS node | | BNS node | | BNS node | | BNS node |
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+----------+ +----------+ +----------+ +----------+
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^ ^ ^ ^
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| (indexing | | |
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| blockchain) | | |
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+---------------------------------------------------------------+
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Blockchain | Blockchain Peer Network |
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+---------------------------------------------------------------+
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Figure 1: Location of Atlas in the Blockstack architecture. Each BNS node
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implements an Atlas peer. An Atlas peer treats a name state value in BNS as
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the hash of a DNS zone file. Atlas peers exchange zone files with one another
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until they each have a full replica of all known zone files. Clients can look
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up zone files for names using the name's stat value as a zone file hash. Clients
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can broadcast zone files to the network if they match a previously-announced
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hash. In practice, zone files store URLs to a name owner's Gaia hubs, thereby
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allowing Blockstack apps to read and write data in Gaia.
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```
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Nevertheless, Atlas is a general-purpose content-addressed storage
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system that advanced developers can use to **host data in an immutable
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and durable manner.** Beyond its default use-case in Blockstack,
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Atlas is ideal for tasks like:
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* Announcing PGP public keys under a human-readable name
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* Storing package hashes for a software release
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* Securely deploying shell scripts to remote VMs
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* Binding human-readable names to Tor .onion addresses
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([example](https://github.com/blockstack-packages/blockstack-tor))
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## Motivation
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Atlas was designed to augment BNS. BNS allows each name to store a small
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amount of state---on the order of 20 bytes. The size is so small because the
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state must be recorded to a public blockchain, where the cost per byte is
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high and the blockchain protocol limits the size of transactions.
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To compensate for this, we developed an off-chain storage system allows BNS
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names to bind and store a large amount of state to each name in a way that
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*preserves the security properties of having written that state to the
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blockchain*. Instead of storing 20 bytes of data on the blockchain, a BNS name
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owner would store the *cryptograhpic hash* of its state, and then store the actual state
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Atlas. This decouples the name's state size from the blockchain.
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The reference implementation of Atlas currently allows up to 40kb of state to be
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bound to a BNS name, instead of a measly 20 bytes. The 40kb of data is
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replicated to each BNS node, where it is stored forever.
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## Feature Comparison
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Atlas is not the only peer-to-peer content-addressible chunk store in existance. The following
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feature table describes Atlas in relation to other popular chunk stores.
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| **Features** | Atlas | BitTorrent | [DAT](https://datproject.org/) | [IPFS](https://ipfs.io) | [Swarm](https://github.com/ethersphere/swarm) |
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|-----------------------------|-------|------------|--------------------------------|-------------------------|-----------------------------------------------|
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| Each peer stores all chunks | X | X | | | |
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| Replicas are permanent [1] | X | X | X | | |
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| Replicas are free | | X | X | X | |
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| Sybil-resistant chunk discovery | X | X | | | X |
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| Sybil-resistant peer discovery | X | | | | |
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| Fixed chunk size | X | | X | X | X |
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[1] Here, "permanent" means that once a peer has data, they will never evict it
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as part of the protocol.
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