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storj/docs/blueprints/storage-node-satellite-selection.md
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Storage Node Satellite Selection

Abstract

This document details an enhanced method of Satellite selection and maintenance for Storage Node operators.

Background.

With the removal of Kademlia, Storage Nodes need a way to identify and select Satellite's with whom to interact. The implementation of Satellite selection is currently accomplished via a list of whitelisted Satellite URLs in the configuration file. The list defaults to well-known satellites hard-coded into the storage node binary. This method is simple and easy to configure at first time setup, but unfortunately requires manual maintenance of the list going forward.

The ideal solution would be just as easy to set up in the common case while removing the burden of future maintenance.

Design

The proposed design is to discover trusted Satellites from externally maintained lists from trusted sources with the ability to manually trust/block Satellites.

Concepts

Satellite URL

A Satellite URL holds all the information needed to contact and identify a Satellite. It is comprised of an optional scheme (i.e. storj://), an ID, and an address.

The address MUST contain both a host and port for the purposes of this feature.

The following are all examples of valid Satellite URLs:

12EayRS2V1kEsWESU9QMRseFhdxYxKicsiFmxrsLZHeLUtdps3S@us-central-1.tardigrade.io:7777
storj://12EayRS2V1kEsWESU9QMRseFhdxYxKicsiFmxrsLZHeLUtdps3S@us-central-1.tardigrade.io:7777

The following are invalid Satellite URLs (missing or partial IDs):

us-central-1.tardigrade.io:7777
12EayRS2@us-central-1.tardigrade.io:7777
storj://us-central-1.tardigrade.io:7777
storj://12EayRS2@us-central-1.tardigrade.io:7777

Trusted Satellite List

The Trusted Satellite List is a text document where each line represents the Satellite URL of a trusted Satellite.

12EayRS2V1kEsWESU9QMRseFhdxYxKicsiFmxrsLZHeLUtdps3S@us-central-1.tardigrade.io:7777
121RTSDpyNZVcEU84Ticf2L1ntiuUimbWgfATz21tuvgk3vzoA6@asia-east-1.tardigrade.io:7777

Storage Node Configuration

The Storage Node configuration for Satellite selection is a list of one or more entries, where each entry is one of the following:

  • Trusted Satellite List URL
  • Trusted Satellite URL
  • Untrusted Satellite URL

Trusted Satellite List URL Entry

This entry contains a URL where a Trusted Satellite List can be downloaded.

Supported schemes are file://, http:// and https://. When using HTTP an https:// URL should be preferred over an http:// URL to ensure transport security and prevent a person-in-the-middle from tampering with the list.

Examples:

https://www.tardigrade.io/trusted-satellites
file:///some/path/to/trusted-satellites.txt

Trusted Satellite URL Entry

This entry contains the URL to an explicitly trusted Satellite. The format of the entry is a Satellite URL.

Untrusted Satellite Entry

This entry contains the URL to an explicitly untrusted Satellite. The format of the entry is a ! followed by one of the following:

  • Satellite ID followed by an @ (to distinguish it from a host)
!121RTSDpyNZVcEU84Ticf2L1ntiuUimbWgfATz21tuvgk3vzoA6@
  • Satellite host. If the host is a domain, then subdomains are also untrusted (i.e. !tardigrade.io will block us-central-1.tardigrade.io)
!tardigrade.io
!us-central-1.tardigrade.io
!us-east-1.tardigrade.io
  • Satellite URL
!121RTSDpyNZVcEU84Ticf2L1ntiuUimbWgfATz21tuvgk3vzoA6@us-central-1.tardigrade.io:7777

Building the List of Trusted Satellite URLs

To build the list of trusted Satellite URLs each entry in the configuration is traversed in order, parsed, and processed accordingly:

  1. If the entry begins with a !, it represents an untrusted Satellite entry. It is added to the untrusted list, which is used later.
  2. If the entry begins with file://, http://, or https://, it is a Trusted Satellite List URL. The URL is used to fetch a list of Trusted Satellite URLs that are added into the trusted list.
  3. If the entry begins with storj://, or otherwise does not use a scheme, it is a trusted Satellite URL entry. It is added into the trusted list.
  4. If an entry does not match any of the above, it is a configuration error.

If a Trusted Satellite List cannot be fetched a warning should be logged. If available, the last known copy from the Trusted Satellite List URL should be used. Storage Nodes should attempt to persist the downloaded lists. If they cannot, a warning should be logged.

After all configuration entries have been processed, each URL in the trusted list is checked against the untrusted list and removed if it matches an entry . An untrusted entry matches a URL using the following criteria:

  • When the untrusted entry is just a Satellite ID, it matches any URL with that ID.
  • When the untrusted entry is just a host, it matches any URL with the same host. If the host is a domain name, then the entry also matches URLs within a subdomain of that host.
  • When the untrusted entry is a full Satellite URL, it matches any URL that is equal.

After the trusted list has been pruned, the remaining URLs are aggregated according to the following rules:

  • A Satellite URL is considered authoritative if it matches either of the following criteria:
    • Configured via a Trusted Satellite URL entry
    • Configured via a file:// URL
    • Configured via an https:// or http:// Trusted Satellite List URL AND matches the domain or is a subdomain of the domain name in the Trusted Satellite List URL.
  • Satellite URLs are equivalent if the address portions are equal.
  • When aggregating equivalent Satellite URLs (i.e. address matches) with differing IDs, the authoritative Satellite URL wins. If neither or both are authoritative, the one aggregated first wins.

Example

Consider the following Trusted Satellite List URLs and their contents. For brevity sake, the full ID of each URL is being shortened (real configurations MUST specify the full ID).

  • file:///path/to/some/trusted-satellites.txt
1@bar.test:7777
  • https://foo.test/trusted-satellites
2@f.foo.test:7777
2@buz.test:7777
2@qiz.test:7777
5@ohno.test:7777
  • https://bar.test/trusted-satellites
3@f.foo.test:7777
3@bar.test:7777
3@baz.test:7777
3@buz.test:7777
3@quz.test:7777
  • https://baz.test/trusted-satellites
4@baz.test:7777
4@qiz.test:7777
4@subdomain.quz.test:7777

Now consider the following configuration:

- !quz.test
- file:///path/to/some/trusted-satellites.txt
- https://foo.test/trusted-satellites
- https://bar.test/trusted-satellites
- https://baz.test/trusted-satellites
- 0@f.foo.test:7777
- !2@qiz.test:7777
- !5

After expanding each entry, we have the following unaggregated trusted list:

1@bar.test:7777                   (authoritative due to file:// URL)
2@f.foo.test:7777                 (authoritative due to foo.test domain)
2@buz.test:7777
2@qiz.test:7777
5@ohno.test:7777
3@f.foo.test:7777
3@bar.test:7777                   (authoritative due to bar.test domain)
3@baz.test:7777
3@buz.test:7777
3@quz.test:7777
4@baz.test:7777                   (authoritative due to baz.test domain)
4@qiz.test:7777
4@subdomain.quz.test:7777
0@f.foo.test:7777                 (authoritative due to explicit configuration)

And the following untrusted list:

quz.test
2@qiz.test:7777
5@

The trusted list is pruned with the untrusted list, leaving the following trusted list:

1@bar.test:7777                   (authoritative due to file:// URL)
2@f.foo.test:7777                 (authoritative due to foo.test domain)
2@buz.test:7777
3@f.foo.test:7777
3@bar.test:7777                   (authoritative due to bar.test domain)
3@baz.test:7777
3@buz.test:7777
4@baz.test:7777                   (authoritative due to baz.test domain)
4@qiz.test:7777
0@f.foo.test:7777                 (authoritative due to explicit configuration)

We aggregate from top to bottom (i.e. in the order they were specified/fetched) and are left with the following:

1@bar.test:7777
2@f.foo.test:7777
2@buz.test:7777
4@baz.test:7777
4@qiz.test:7777
  • 1@bar.test:7777 was selected because even though 3@bar.test:7777 was also authoritative, 1@bar.test:7777 came first.
  • 2@f.foo.test:7777 was selected because it was authoritative over 3@f.foo.test:7777 and came before 0@f.foo.test.
  • 2@buz.test:7777 was selected because it came before 3@buz.test:7777 (neither was authoritative)
  • 4@baz.test:7777 was selected it was authoritative over 3@baz.test:7777, even though the latter came first.
  • 4@qiz.test:7777 was selected because it was the only URL for qiz.test:7777

Rebuilding the List of Trusted Satellite URLs

The list of trusted Satellite URLs should be recalculated daily (with some jitter).

Backwards Compatibility

The old piecestore configuration (i.e. piecestore.OldConfig) currently contains a comma separated list of trusted Satellite URLs (WhitelistedSatellites). It defaults to the current list of known good satellites. On startup, if the new configuration is unset, then the old configuration should be used to form a fixed set of trusted Satellite URLs.

Open Issues

  • How long should storage nodes use cached/persisted lists for? Should lists be persisted at all?
  • If aggregation yields no URLs (list URL unreachable) should we default to anything? How should this be reported?
  • If block listing removes all URLs, how should this be reported?
  • Can we safely auto-migrate storage nodes into this new method of management?
  • How long does the storage node wait before garbage collecting pieces from Satellites it no longer trusts? Should this be manual operation?

To Do

  • Implement an endpoint at https://www.tardigrade.io/trusted-satellites to return the default list of trusted Satellites.
  • Implement a trust.ListConfig configuration struct which:
    • Contains the list of entries (with a release default of a single list containing https://www.tardigrade.io/trusted-satellites)
    • Contains a refresh interval
    • Maintains backwards compatibility with WhitelistedSatellites in piecestore.OldConfig
  • Implement storj.io/storj/storagenode/trust.List that:
    • Consumes trust.ListConfig for configuration
    • Performs the initial fetching and building of trusted Satellite URLs
    • Updates according to the refresh interval (with jitter)
  • Refactor storj.io/storj/storagenode/trust.Pool to use trust.List