⚠️ This repo was moved to https://github.com/ssbc/ssb-replication-scheduler. This archival will remain in this GitHub org ssb-ngi-pointer to demonstrate the outcome of the work done by the SSB NGI Pointer team during 2020 and 2021. The SSB NGI Pointer team is no longer active because we completed our grant project.

ssb-replication-scheduler

Triggers replication of feeds identified as friendly in the social graph.

Depends on ssb-friends APIs, and calls ssb-ebt APIs.

Installation

Prerequisites:

• Requires Node.js 10 or higher
• Requires ssb-db or ssb-db2
• Requires ssb-friends version 5.0 or higher
• Requires ssb-ebt version 7.0 or higher

npm install --save ssb-replication-scheduler

Add this secret-stack plugin like this:

 const SecretStack = require('secret-stack')
 const caps = require('ssb-caps')

 const createSsbServer = SecretStack({ caps })
     .use(require('ssb-master'))
     .use(require('ssb-db2'))
     .use(require('ssb-ebt'))
     .use(require('ssb-friends'))
+    .use(require('ssb-replication-scheduler'))
     .use(require('ssb-conn'))
     // ...

Usage

Typically there is nothing you need to do after installing this plugin. As soon as the SSB peer is initialized, ssb-replication-scheduler will automatically query the social graph, and either request replication or stop replication, depending whether the feed is friendly or blocked.

Opinions embedded in the scheduler:

• Replication is enabled for:
  • The main feed, ssb.id, because this allows you to recover your feed
  • Any friendly feed at a distance of at most config.friends.hops
    • Includes your friends (if config.friends.hops >= 1)
    • Includes friends of friends (if config.friends.hops >= 2)
    • Includes friends of friends of friends (if config.friends.hops >= 3)
    • And so forth
• Replication is strictly disabled for:
  • Any feed you explicitly block

There are two APIs available in case you want to have more control over this module: start() and reconfigure(). Read more about these at the bottom of this file.

Configuration

Some parameters and opinions can be configured by the user or by application code through the conventional ssb-config object. The possible options are listed below:

{
  replicationScheduler: {
    /**
     * Whether the replication scheduler should start automatically as soon as
     * the SSB app is initialized. When `false`, you have to call
     * `ssb.replicationScheduler.start()` manually. Default is `true`.
     */
    autostart: true,

    /**
     * If `partialReplication` is an object, it tells the replication scheduler
     * to perform partial replication, whenever remote feeds support it. If
     * `partialReplication` is `null` (which it is, by default), then all
     * friendly feeds will be requested in full.
     *
     * Read below more about this configuration.
     */
    partialReplication: null,
  }
}

Configuring partial replication

The config.replicationScheduler.partialReplication object describes the tree of meta feeds that we are interested in replicating, for each hops level. For each hops level we have a certain template to describe how replication should work at that level. Notice that this configuration cannot specify who we replicate (that's the job of ssb-friends and your chosen hops, see the Usage section above), this configuration just specifies how should we replicate a friendly peer, in other words, the level of granularity for those peers.

Template per hops

The high-level overview of the partialReplication configuration is:

replicationScheduler: {
  partialReplication: {
    0: TEMPLATE_FOR_HOPS_0,
    1: TEMPLATE_FOR_HOPS_1,
    2: TEMPLATE_FOR_HOPS_2_AND_ABOVE,
  }
}

Soon we'll show how those TEMPLATE_FOR_HOPS work, but for now notice that the highest number will handle all the hops beyond that number, e.g. notice how 2 is the highest number and it means that TEMPLATE_FOR_HOPS_2_AND_ABOVE configures how to replicate peers at hops 2 or 3 or 4 or higher. There's nothing special about the number 2, it could also have been this:

replicationScheduler: {
  partialReplication: {
    0: TEMPLATE_FOR_HOPS_0,
    1: TEMPLATE_FOR_HOPS_1_AND_ABOVE,
  }
}

Or even this (which means we use the same template for all peers, regardless of their hops distance):

replicationScheduler: {
  partialReplication: {
    0: TEMPLATE_FOR_HOPS_0_AND_ABOVE,
  }
}

Or even fractional numbers:

replicationScheduler: {
  partialReplication: {
    0: TEMPLATE_FOR_HOPS_0,
    0.5: TEMPLATE_FOR_HOPS_HALF,
    1: TEMPLATE_FOR_HOPS_1_AND_ABOVE,
  }
}

Template structure

A Template is JSON which describes how should we do partial replication. If the template is null or a falsy value, then it means that for that hops level we don't do partial replication and we will do full replication (which means pre-2022 SSB replication of the peer's main feed).

When the template is a JSON tree of objects and arrays, where the root of the tree is always the root meta feed. The template describes which keys in the metafeeds and subfeeds must match exactly the values given. So that if we write feedpurposes: 'indexes', it means we are interested in matching the metafeed that has the field feedpurposes exactly matching the value "indexes". All specified fields must match, but omitted fields are allowed to be any value.

The field subfeeds is not matching an actual field, instead, it is assumes we are dealing with a meta feed and this is describing its subfeeds that we would like to replicate.

Special variables

Some keys and some values are special, in the sense that they are not taken literally, but are going to be substituted by other context-relative values. These special variables are always prefixed with $.

• Special keys
  • $format
• Special values
  • $main
  • $root

The field key $format refers to ssb-ebt "replication formats" and can be included in a template to specify which replication format to use in ssb-ebt. The value of this field should be the format's name as a string.

If the value of a field, e.g. in ssb-ql-0 queries, are the special strings "$main" or "$root", then they respectively refer to the IDs of the main feed and of the root meta feed.

Example

In the example below, we set up partial replication with the meaning:

• For hops 0 (that is, "yourself"), replicate some app feeds and all index feeds
• For hops 1 (direct friends), replicate only 5 specific index feeds
• For hops 2 and beyond, replicate only 2 specific index feeds

partialReplication: {
  0: {
    subfeeds: [
      { feedpurpose: 'coolgame' },
      { feedpurpose: 'git-ssb' },
      {
        feedpurpose: 'indexes',
        subfeeds: [
          {
            feedpurpose: 'index',
            $format: 'indexed',
          },
        ],
      },
    ],
  },

  1: {
    subfeeds: [
      {
        feedpurpose: 'indexes',
        subfeeds: [
          {
            feedpurpose: 'index',
            metadata: {
              querylang: 'ssb-ql-0',
              query: { author: '$main', type: null, private: true },
            },
            $format: 'indexed',
          },
          {
            feedpurpose: 'index',
            metadata: {
              querylang: 'ssb-ql-0',
              query: { author: '$main', type: 'post', private: false },
            },
            $format: 'indexed',
          },
          {
            feedpurpose: 'index',
            metadata: {
              querylang: 'ssb-ql-0',
              query: { author: '$main', type: 'vote', private: false },
            },
            $format: 'indexed',
          },
          {
            feedpurpose: 'index',
            metadata: {
              querylang: 'ssb-ql-0',
              query: { author: '$main', type: 'about', private: false },
            },
            $format: 'indexed',
          },
          {
            feedpurpose: 'index',
            metadata: {
              querylang: 'ssb-ql-0',
              query: { author: '$main', type: 'contact', private: false },
            },
            $format: 'indexed',
          },
        ],
      },
    ],
  },

  2: {
    subfeeds: [
      {
        feedpurpose: 'indexes',
        subfeeds: [
          {
            feedpurpose: 'index',
            metadata: {
              querylang: 'ssb-ql-0',
              query: { author: '$main', type: 'about', private: false },
            },
            $format: 'indexed',
          },
          {
            feedpurpose: 'index',
            metadata: {
              querylang: 'ssb-ql-0',
              query: { author: '$main', type: 'contact', private: false },
            },
            $format: 'indexed',
          },
        ],
      },
    ],
  },
}

APIs

ssb.replicationScheduler.start() => void (sync)

ssb.replicationScheduler.reconfigure(config) => void (sync)

At any point during the execution of your program, you can reconfigure the replication rules using this API. The configuration object passed to this API has the same shape as config.replicationScheduler (see above) has.

License

LGPL-3.0