# Connection Profile¶

Audience: Architects, application and smart contract developers

A connection profile describes a set of components, including peers, orderers and certificate authorities in a Hyperledger Fabric blockchain network. It also contains channel and organization information relating to these components. A connection profile is primarily used by an application to configure a gateway that handles all network interactions, allowing it to focus on business logic. A connection profile is normally created by an administrator who understands the network topology.

In this topic, we’re going to cover:

## Scenario¶

A connection profile is used to configure a gateway. Gateways are important for many reasons, the primary being to simplify an application’s interaction with a network channel.

Two applications, issue and buy, use gateways 1&2 configured with connection profiles 1&2. Each profile describes a different subset of MagnetoCorp and DigiBank network components. Each connection profile must contain sufficient information for a gateway to interact with the network on behalf of the issue and buy applications. See the text for a detailed explanation.

A connection profile contains a description of a network view, expressed in a technical syntax, which can either be JSON or YAML. In this topic, we use the YAML representation, as it’s easier for you to read. Static gateways need more information than dynamic gateways because the latter can use service discovery to dynamically augment the information in a connection profile.

A connection profile should not be an exhaustive description of a network channel; it just needs to contain enough information sufficient for a gateway that’s using it. In the network above, connection profile 1 needs to contain at least the endorsing organizations and peers for the issue transaction, as well as identifying the peers that will notify the gateway when the transaction has been committed to the ledger.

It’s easiest to think of a connection profile as describing a view of the network. It could be a comprehensive view, but that’s unrealistic for a few reasons:

• Peers, orderers, certificate authorities, channels, and organizations are added and removed according to demand.
• Components can start and stop, or fail unexpectedly (e.g. power outage).
• A gateway doesn’t need a view of the whole network, only what’s necessary to successfully handle transaction submission or event notification for example.
• Service Discovery can augment the information in a connection profile. Specifically, dynamic gateways can be configured with minimal Fabric topology information; the rest can be discovered.

A static connection profile is normally created by an administrator who understands the network topology in detail. That’s because a static profile can contain quite a lot of information, and an administrator needs to capture this in the corresponding connection profile. In contrast, dynamic profiles minimize the amount of definition required and therefore can be a better choice for developers who want to get going quickly, or administrators who want to create a more responsive gateway. Connection profiles are created in either the YAML or JSON format using an editor of choice.

## Usage¶

We’ll see how to define a connection profile in a moment; let’s first see how it is used by a sample MagnetoCorp issue application:

const yaml = require('js-yaml');
const { Gateway } = require('fabric-network');

const gateway = new Gateway();

await gateway.connect(connectionProfile, connectionOptions);


After loading some required classes, see how the paperNet.yaml gateway file is loaded from the file system, converted to a JSON object using the yaml.safeLoad() method, and used to configure a gateway using its connect() method.

By configuring a gateway with this connection profile, the issue application is providing the gateway with the relevant network topology it should use to process transactions. That’s because the connection profile contains sufficient information about the PaperNet channels, organizations, peers, orderers and CAs to ensure transactions can be successfully processed.

It’s good practice for a connection profile to define more than one peer for any given organization – it prevents a single point of failure. This practice also applies to dynamic gateways; to provide more than one starting point for service discovery.

A DigiBank buy application would typically configure its gateway with a similar connection profile, but with some important differences. Some elements will be the same, such as the channel; some elements will overlap, such as the endorsing peers. Other elements will be completely different, such as notification peers or certificate authorities for example.

The connectionOptions passed to a gateway complement the connection profile. They allow an application to declare how it would like the gateway to use the connection profile. They are interpreted by the SDK to control interaction patterns with network components, for example to select which identity to connect with, or which peers to use for event notifications. Read about the list of available connection options and when to use them.

## Structure¶

To help you understand the structure of a connection profile, we’re going to step through an example for the network shown above. Its connection profile is based on the PaperNet commercial paper sample, and stored in the GitHub repository. For convenience, we’ve reproduced it below. You will find it helpful to display it in another browser window as you now read about it:

• Line 9: name: "papernet.magnetocorp.profile.sample"

This is the name of the connection profile. Try to use DNS style names; they are a very easy way to convey meaning.

• Line 16: x-type: "hlfv1"

Users can add their own x- properties that are “application-specific” – just like with HTTP headers. They are provided primarily for future use.

• Line 20: description: "Sample connection profile for documentation topic"

A short description of the connection profile. Try to make this helpful for the reader who might be seeing this for the first time!

• Line 25: version: "1.0"

The schema version for this connection profile. Currently only version 1.0 is supported, and it is not envisioned that this schema will change frequently.

• Line 32: channels:

This is the first really important line. channels: identifies that what follows are all the channels that this connection profile describes. However, it is good practice to keep different channels in different connection profiles, especially if they are used independently of each other.

• Line 36: papernet:

Details of papernet, the first channel in this connection profile, will follow.

• Line 41: orderers:

Details of all the orderers for papernet follow. You can see in line 45 that the orderer for this channel is orderer1.magnetocorp.example.com. This is just a logical name; later in the connection profile (lines 134 - 147), there will be details of how to connect to this orderer. Notice that orderer2.digibank.example.com is not in this list; it makes sense that applications use their own organization’s orderers, rather than those from a different organization.

• Line 49: peers:

Details of all the peers for papernet will follow.

You can see three peers listed from MagnetoCorp: peer1.magnetocorp.example.com, peer2.magnetocorp.example.com and peer3.magnetocorp.example.com. It’s not necessary to list all the peers in MagnetoCorp, as has been done here. You can see only one peer listed from DigiBank: peer9.digibank.example.com; including this peer starts to imply that the endorsement policy requires MagnetoCorp and DigiBank to endorse transactions, as we’ll now confirm. It’s good practice to have multiple peers to avoid single points of failure.

Underneath each peer you can see four non-exclusive roles: endorsingPeer, chaincodeQuery, ledgerQuery and eventSource. See how peer1 and peer2 can perform all roles as they host papercontract. Contrast to peer3, which can only be used for notifications, or ledger queries that access the blockchain component of the ledger rather than the world state, and hence do not need to have smart contracts installed. Notice how peer9 should not be used for anything other than endorsement, because those roles are better served by MagnetoCorp peers.

Again, see how the peers are described according to their logical names and their roles. Later in the profile, we’ll see the physical information for these peers.

• Line 97: organizations:

Details of all the organizations will follow, for all channels. Note that these organizations are for all channels, even though papernet is currently the only one listed. That’s because organizations can be in multiple channels, and channels can have multiple organizations. Moreover, some application operations relate to organizations rather than channels. For example, an application can request notification from one or all peers within its organization, or all organizations within the network – using connection options. For this, there needs to be an organization to peer mapping, and this section provides it.

• Line 101: MagnetoCorp:

All peers that are considered part of MagnetoCorp are listed: peer1, peer2 and peer3. Likewise for Certificate Authorities. Again, note the logical name usages, the same as the channels: section; physical information will follow later in the profile.

• Line 121: DigiBank:

Only peer9 is listed as part of DigiBank, and no Certificate Authorities. That’s because these other peers and the DigiBank CA are not relevant for users of this connection profile.

• Line 134: orderers:

The physical information for orderers is now listed. As this connection profile only mentioned one orderer for papernet, you see orderer1.magnetocorp.example.com details listed. These include its IP address and port, and gRPC options that can override the defaults used when communicating with the orderer, if necessary. As with peers:, for high availability, specifying more than one orderer is a good idea.

• Line 152: peers:

The physical information for all previous peers is now listed. This connection profile has three peers for MagnetoCorp: peer1, peer2, and peer3; for DigiBank, a single peer peer9 has its information listed. For each peer, as with orderers, their IP address and port is listed, together with gRPC options that can override the defaults used when communicating with a particular peer, if necessary.

• Line 194: certificateAuthorities:

The physical information for certificate authorities is now listed. The connection profile has a single CA listed for MagnetoCorp, ca1-magnetocorp, and its physical information follows. As well as IP details, the registrar information allows this CA to be used for Certificate Signing Requests (CSR). These are used to request new certificates for locally generated public/private key pairs.

Now you’ve understood a connection profile for MagnetoCorp, you might like to look at a corresponding profile for DigiBank. Locate where the profile is the same as MagnetoCorp’s, see where it’s similar, and finally where it’s different. Think about why these differences make sense for DigiBank applications.

That’s everything you need to know about connection profiles. In summary, a connection profile defines sufficient channels, organizations, peers, orderers and certificate authorities for an application to configure a gateway. The gateway allows the application to focus on business logic rather than the details of the network topology.

## Sample¶

This file is reproduced inline from the GitHub commercial paper sample.

1: ---
2: #
3: # [Required]. A connection profile contains information about a set of network
4: # components. It is typically used to configure gateway, allowing applications
5: # interact with a network channel without worrying about the underlying
6: # topology. A connection profile is normally created by an administrator who
7: # understands this topology.
8: #
9: name: "papernet.magnetocorp.profile.sample"
10: #
11: # [Optional]. Analogous to HTTP, properties with an "x-" prefix are deemed
12: # "application-specific", and ignored by the gateway. For example, property
13: # "x-type" with value "hlfv1" was originally used to identify a connection
14: # profile for Fabric 1.x rather than 0.x.
15: #
16: x-type: "hlfv1"
17: #
18: # [Required]. A short description of the connection profile
19: #
20: description: "Sample connection profile for documentation topic"
21: #
22: # [Required]. Connection profile schema version. Used by the gateway to
23: # interpret these data.
24: #
25: version: "1.0"
26: #
27: # [Optional]. A logical description of each network channel; its peer and
28: # orderer names and their roles within the channel. The physical details of
29: # these components (e.g. peer IP addresses) will be specified later in the
30: # profile; we focus first on the logical, and then the physical.
31: #
32: channels:
33:   #
34:   # [Optional]. papernet is the only channel in this connection profile
35:   #
36:   papernet:
37:     #
38:     # [Optional]. Channel orderers for PaperNet. Details of how to connect to
39:     # them is specified later, under the physical "orderers:" section
40:     #
41:     orderers:
42:     #
43:     # [Required]. Orderer logical name
44:     #
45:       - orderer1.magnetocorp.example.com
46:     #
47:     # [Optional]. Peers and their roles
48:     #
49:     peers:
50:     #
51:     # [Required]. Peer logical name
52:     #
53:       peer1.magnetocorp.example.com:
54:         #
55:         # [Optional]. Is this an endorsing peer? (It must have chaincode
56:         # installed.) Default: true
57:         #
58:         endorsingPeer: true
59:         #
60:         # [Optional]. Is this peer used for query? (It must have chaincode
61:         # installed.) Default: true
62:         #
63:         chaincodeQuery: true
64:         #
65:         # [Optional]. Is this peer used for non-chaincode queries? All peers
66:         # support these types of queries, which include queryBlock(),
67:         # queryTransaction(), etc. Default: true
68:         #
69:         ledgerQuery: true
70:         #
71:         # [Optional]. Is this peer used as an event hub? All peers can produce
72:         # events. Default: true
73:         #
74:         eventSource: true
75:       #
76:       peer2.magnetocorp.example.com:
77:         endorsingPeer: true
78:         chaincodeQuery: true
79:         ledgerQuery: true
80:         eventSource: true
81:       #
82:       peer3.magnetocorp.example.com:
83:         endorsingPeer: false
84:         chaincodeQuery: false
85:         ledgerQuery: true
86:         eventSource: true
87:       #
88:       peer9.digibank.example.com:
89:         endorsingPeer: true
90:         chaincodeQuery: false
91:         ledgerQuery: false
92:         eventSource: false
93: #
94: # [Required]. List of organizations for all channels. At least one organization
95: # is required.
96: #
97: organizations:
98:    #
99:    # [Required]. Organizational information for MagnetoCorp
100:   #
101:   MagnetoCorp:
102:     #
103:     # [Required]. The MSPID used to identify MagnetoCorp
104:     #
105:     mspid: MagnetoCorpMSP
106:     #
107:     # [Required]. The MagnetoCorp peers
108:     #
109:     peers:
110:       - peer1.magnetocorp.example.com
111:       - peer2.magnetocorp.example.com
112:       - peer3.magnetocorp.example.com
113:     #
114:     # [Optional]. Fabric-CA Certificate Authorities.
115:     #
116:     certificateAuthorities:
117:       - ca-magnetocorp
118:   #
119:   # [Optional]. Organizational information for DigiBank
120:   #
121:   DigiBank:
122:     #
123:     # [Required]. The MSPID used to identify DigiBank
124:     #
125:     mspid: DigiBankMSP
126:     #
127:     # [Required]. The DigiBank peers
128:     #
129:     peers:
130:       - peer9.digibank.example.com
131: #
132: # [Optional]. Orderer physical information, by orderer name
133: #
134: orderers:
135:   #
136:   # [Required]. Name of MagnetoCorp orderer
137:   #
138:   orderer1.magnetocorp.example.com:
139:     #
140:     # [Required]. This orderer's IP address
141:     #
142:     url: grpc://localhost:7050
143:     #
144:     # [Optional]. gRPC connection properties used for communication
145:     #
146:     grpcOptions:
147:       ssl-target-name-override: orderer1.magnetocorp.example.com
148: #
149: # [Required]. Peer physical information, by peer name. At least one peer is
150: # required.
151: #
152: peers:
153:   #
154:   # [Required]. First MagetoCorp peer physical properties
155:   #
156:   peer1.magnetocorp.example.com:
157:     #
158:     # [Required]. Peer's IP address
159:     #
160:     url: grpc://localhost:7151
161:     #
162:     # [Optional]. gRPC connection properties used for communication
163:     #
164:     grpcOptions:
165:       ssl-target-name-override: peer1.magnetocorp.example.com
166:       request-timeout: 120001
167:   #
168:   # [Optional]. Other MagnetoCorp peers
169:   #
170:   peer2.magnetocorp.example.com:
171:     url: grpc://localhost:7251
172:     grpcOptions:
173:       ssl-target-name-override: peer2.magnetocorp.example.com
174:       request-timeout: 120001
175:   #
176:   peer3.magnetocorp.example.com:
177:     url: grpc://localhost:7351
178:     grpcOptions:
179:       ssl-target-name-override: peer3.magnetocorp.example.com
180:       request-timeout: 120001
181:   #
182:   # [Required]. Digibank peer physical properties
183:   #
184:   peer9.digibank.example.com:
185:     url: grpc://localhost:7951
186:     grpcOptions:
187:       ssl-target-name-override: peer9.digibank.example.com
188:       request-timeout: 120001
189: #
190: # [Optional]. Fabric-CA Certificate Authority physical information, by name.
191: # This information can be used to (e.g.) enroll new users. Communication is via
192: # REST, hence options relate to HTTP rather than gRPC.
193: #
194: certificateAuthorities:
195:   #
196:   # [Required]. MagnetoCorp CA
197:   #
198:   ca1-magnetocorp:
199:     #
200:     # [Required]. CA IP address
201:     #
202:     url: http://localhost:7054
203:     #
204:     # [Optional]. HTTP connection properties used for communication
205:     #
206:     httpOptions:
207:       verify: false
208:     #
209:     # [Optional]. Fabric-CA supports Certificate Signing Requests (CSRs). A
210:     # registrar is needed to enroll new users.
211:     #
212:     registrar:
215:     #
216:     # [Optional]. The name of the CA.
217:     #
218:     caName: ca-magnetocorp