Access Control: There should be a way to control the access to your data, so that you can decide which peer can access your data with what permissions (read, write, etc.)
Different Runtimes: The replication should work across different devices: your PC, mobile, browser, etc. But all these devices don't have comparable of networking, storage & compute resources.
Restrictive Networks: Firewalls, NATs don't allow all the peers talk to each other. So, we have to come up with new ways to connect peers that live behind these restrictive networks.
In the next couple of posts, we will discuss how we at Dappkit are working to make data replication developer friendly so that you as a developer don't have to think about all these challenges.
This post goes through an example of how today we replicate data between the peers using AvionDB, and our plans to make it much easier than what it is today.
Well, a to-do list is not an app that will make you go nuts, but it does show the process of data replication with an easy to understand application.
The app can be divided into 2 parts:
This is the easy part of the app. We create a simple interface using bootstrap to create, list & update to-do(s).
You can see a QR code too, which we will use for scanning the URL so that you can sync the to-do list on your mobile. You can also use a link that you can directly put in your browser or share it with anyone who wants to sync the to-do list.
Now, we need to use AvionDB to store, list & update the to-do(s) that will be stored locally in your browser.
AvionDB uses IPFS internally to store its data, so we need to import AvionDB & IPFS.
We use the CDN links and add them to the
public/index.html
so that we can access them across the whole application.If you want to use npm modules, here are the modules for AvionDB & IPFS.
Now, we need to initialize AvionDB & IPFS.
This creates a Database named "TodoList", and a Collection named "todos" in it.
Now, we need to add, list & update todo in the "todos" collection.
You can use functions like
insert
or insertOne
to add todo(s).Note that each record that is added in the collection will have an
_id
field added to it automatically, which serves as a unique identifier of the record. You can override the default _id
by adding an _id
field with your record.You can find more information on the functions here.
You can fetch the to-do(s) using functions like
find
& findOne
.This query returns all the to-do(s) in the "todos" collection.
You can find more information on the functions here.
You can update the to-do(s) using functions like
update
, updateMany
, findOneAndUpdate
, etc.This updates the isDone status of a to-do.
You can find more information on the functions here.
Now, as we have created a simple todo app to store, fetch & update the to-do(s), let's see how we can sync/replicate our to-do(s) with multiple devices.
Now before going into the code, let's first understand a few concepts that will help you understand peer-to-peer syncing.
Let's take a real world example.
As we are going through COVID pandemic, Ross & Rachel are attending their classes over the online lectures.
Now, Ross & Rachel want to exchange their notes & do a group study to prepare for their test.
In order to do so, here is what to need to do:
This is very similar to what we are going to do to sync data between the AvionDB peers.
In order to sync the data between any 2 (or more) peers, we need to:
Let's go through each of these points and see how this works under the hood.
Each peer in the network has a unique address that can used to uniquely identify the peer in the network, known as
peerIds
.In case of AvionDB, we use Libp2p (an internal part of IPFS)
peerIds
, which look something like this: Qme499EjQog7UjvuJiduzw1UKMe6hZ1rZ1wQrxz7qpq7TS
.These
peerIds
are generated using a project called Multiformats, which is used to create interoperable, future-proof protocols.You don't need to go too deep into Libp2p or Multiformats. You just need to know that we use the
peerIds
as addresses (email Id, or a mobile number) to identify & communicate with other peers in the network.As we talked about Different Runtimes in the beginning of this post, different devices have different networking, storage & compute resources.
This means that a browser does not have as much networking, storage & compute resources as a PC.
As we talked about the Ross & Rachel example, we saw that we needed to decide on a common platform & language that they could use to communicate.
Similarly, a browser, a PC and a mobile need to decide what common protocols they use so that they can communicate with each other, despite of their differences in networking, storage & compute resources.
A fact that you should know here is that all these platforms support websocket protocol over TCP. So, here websocket is the "common platform or language" that all the devices can use to communicate with each other.
Now, we have the common protocol, but there are restrictive environments such as firewalls & NATs that restrict the peers from discovering each other.
Here is where circuit-relay comes into the picture.
In p2p networks there are many cases where two nodes can't talk to each other directly. That may happen because of network topology, i.e. NATs, or execution environments - for example browser nodes can't connect to each other directly because they lack any sort of socket functionality and relaying on specialized rendezvous nodes introduces an undesirable centralization point to the network. A
circuit-relay
is a way to solve this problem - it is a node that allows two other nodes that can't otherwise talk to each other, use a third node, a relay to do so.How does circuit relay work?
Here is a simple diagram depicting how a typical circuit-relay connection might look:
Peer A
tries to connect to Peer B
but, UH-OH! There is a firewall in between that's preventing it from happening. If both Peer A
and Peer B
know about a relay, they can use it to establish the connection.This is what it looks like, in simplified steps:
Peer A
tries to connect to Peer B
over one of its known addresses.Peer A
and Peer B
know of the same relay - Peer C
Peer A
falls back to dialing over Peer C
to Peer B
using its '/p2p-circuit'
address, which involves:Peer A
sends a HOP
request to Peer C
Relay
extracts the destination address, figures out that a circuit to Peer B
is being requestedRelay
sends a STOP
request to Peer B
Peer B
responds with a SUCCESS
messagePeer A
and Peer B
are now connected over Peer CThat's it!
HOP
and STOP
?Circuit relay consists of two logical parts — dialer/listener and relay (
HOP
). The listener is also known as the STOP
node. Each of these — dial, listen, and relay — happen on a different node. If we use the nodes from the above example, it looks something like this:dialer
knows how to dial a relay
(HOP
) - Node A
relay
(HOP
) knows how to contact a destination node (STOP
) and create a circuit - Relay
nodelistener
(STOP
) knows how to process relay requests that come from the relay (HOP
) node - Node B
Fun fact - the
HOP
and STOP
names are also used internally by circuit to identify the network message types.There are a couple of caveats and features to be aware of:
Relay
will only work if it already has a connection to the STOP
nodemultihop
dialing is supported. It's a feature planed for upcoming releases from Libp2p (no date on this one)multihop
dialing is when several relays are used to establish the connection.A circuit relay address is a multiaddress that describes how to either connect to a peer over a relay (or relays), or allow a peer to announce it is reachable over a particular relay or any relay it is already connected to.
Circuit relay addresses are very flexible and can describe many different aspects of how to establish the relayed connection. In its simplest form, it looks something like this:
/p2p-circuit/ipfs/QmPeer
If we want to be specific as to which transport we want to use to establish the relay, we can encode that in the address as well:
/ip4/127.0.0.1/tcp/65000/ipfs/QmRelay/p2p-circuit/ipfs/QmPeer
This tells us that we want to use
QmRelay
located at address 127.0.0.1 and port 65000./ip4/127.0.0.1/tcp/65000/ipfs/QmRelay/p2p-circuit/ip4/127.0.0.1/tcp/8080/ws/ipfs/QmPeer
We can take it a step further and encode the same information for the destination peer. In this case, we have it located at 127.0.0.1 on port 8080 and using a Web sockets transport!
/ip4/127.0.0.1/tcp/65000/ipfs/QmRelay/p2p-circuit
If a node is configured with this address, it will use the specified host (
/ip4/127.0.0.1/tcp/65000/ipfs/QmRelay
) as a relay and it will be reachable over this relay.There could multiple addresses of this sort specified in the config, in which case the node will be reachable over all of them.This is useful if, for example, the node is behind a firewall but wants to be reachable from the outside over a specific relay.
Other use-cases are also supported by this scheme, e.g. we can have multiple hops (circuit-relay nodes) encoded in the address, something planed for future releases.
In our to-do list example we created a relay peer with the following multiaddress:
/dnsaddr/node1.dappkit.io/tcp/6969/wss/p2p/QmfLwmXF25u1n5pD8yXcbmZew3td66qPU1FroWNrkxS4bt
You can use this relay to connect your peers too!
Now as we have discussed how to get through different runtimes & restrictive networks, let's now move on to see how to establish a connection.
In order to connect to any peer using IPFS, we have a function
ipfs.swarm.connect(multiaddress)
where multiaddress
is the address of any peer that a peer wants to connect to.So, for example if
Peer A
wants to connect to the relay – Peer C
then we will do something like this:After, we have connected
Peer A
& Peer B
with the relay – Peer C
we can now use the /p2p-circuit
address of Peer B
to connect to Peer A
or vice-versa.Voila! You have now connected the peers 🎉 Now we just need to replicate the data between the 2 peers.
In order to sync data between the peers, we need the database address of the “TodoList” database & the name of the collection that we created above.
To get this information we need to communicate this data between the peers. For this, we use something called Publish/Subscribe
Publish/Subscribe is a system where peers congregate around topics they are interested in. Peers interested in a topic are said to be subscribed to that topic:
Peers can send messages to topics. Each message gets delivered to all peers subscribed to the topic:
So, if we create a topic:
peerId
of Peer A
so that anyone who is subscribed to peerId
of Peer A
can get the messages from Peer A
. This way Peer A
can publish the database address of the "TodoList" database & the name of the collection to all its subscribers in one go!Here is the example code showing
Peer B
subscribed to Peer A
using its peerId
and using the published message (msg
) to open the database & the collection.Here is an example code showing
Peer A
publishing the message (msg
) to the topic peerIdA
.And that’s it! This is how we currently sync data between peers in AvionDB.
Here is a working demo of the to-do list app.
Here are some useful links:
But this is not something we want you to go through when you are creating your application. We want to give developers a simple way to sync data that abstracts away all this complexity of different runtimes, restrictive networks, etc.
So we are working on making this a better experience for the developers so that they can focus on building applications rather than tackling these core issues.
If you want to keep a close track of our progress then feel free to reach us out on our Discord server.
NOTE: We have not talked about Access Control in this post, but we have a ton of examples already built for different Web 2.0 & Web 3.0 based access control. Feel free to check them out here. We will be back with posts on access controller too. Meanwhile, if you have any questions, feel free to reach us out on our Discord server.