一、Fabric网络组织
Fabric网络组织按如下结构组成：Fabric网络-->Channel通道-->组织（成员）-->节点。即整个网络由数个通道组成，每个通道都由多个组织构成，而每个组织内部由数个节点组成（可能由功能或其他划分方式分为多个节点）。如下图所示：
一个组织（其实是成员）在一个通道上可以有多个Peer节点，这时候为了提高通信效率，需要选举出来一个主节点（leader）作为代表和排序服务节点通信，负责从排序服务节点处获取最新的区块并在组织内部同步。有如下两种方式：
1. 静态指定配置文件中配置
# Gossip related configuration gossip: # Defines whenever peer will initialize dynamic algorithm for # "leader" selection, where leader is the peer to establish # connection with ordering service and use delivery protocol # to pull ledger blocks from ordering service useLeaderElection: false # Statically defines peer to be an organization "leader", # where this means that current peer will maintain connection # with ordering service and disseminate block across peers in # its own organization orgLeader: true 2. 动态选举相关配置：
# Gossip related configuration gossip: # Leader election service configuration election: # Longest time peer wait for stable membership during leader election startup (unit: second) startupGracePeriod: 15s # Interval gossip membership sampled to check its stability (unit: second) membershipSampleInterval: 1s # Time pass since last declaration message before peer decide to go to election (unit: second) leaderAliveThreshold: 10s # Time between peer sends propose message and declare itself as a leader (sends declaration message) (unit: second) leaderElectionDuration: 5s 3. leader节点选举流程选举流程（简要）：
如果当前没有leader，进入选举算法 如果当前是leader:广播leadership declearation，如果收到比自己小的leadership declearation，自己变为follower; 如果当前是follower:指定时间内没有收到leadership declearation，则认为leader离线了，进入选举流程选举算法（简要）:
广播提议自己为leader消息 各个节点收集选举消息 比对ID，如果自己ID最小，则自己为leader详细过程如下图所示：
伪代码实现：
// Gossip leader election module // Algorithm properties: // - Peers break symmetry by comparing IDs // - Each peer is either a leader or a follower, // and the aim is to have exactly 1 leader if the membership view // is the same for all peers // - If the network is partitioned into 2 or more sets, the number of leaders // is the number of network partitions, but when the partition heals, // only 1 leader should be left eventually // - Peers communicate by gossiping leadership proposal or declaration messages // The Algorithm, in pseudo code: // // // variables: // leaderKnown = false // // Invariant: // Peer listens for messages from remote peers // and whenever it receives a leadership declaration, // leaderKnown is set to true // // Startup(): // wait for membership view to stabilize, or for a leadership declaration is received // or the startup timeout expires. // goto SteadyState() // // SteadyState(): // while true: // If leaderKnown is false: // LeaderElection() // If you are the leader: // Broadcast leadership declaration // If a leadership declaration was received from // a peer with a lower ID, // become a follower // Else, you're a follower: // If haven't received a leadership declaration within // a time threshold: // set leaderKnown to false // // LeaderElection(): // Gossip leadership proposal message // Collect messages from other peers sent within a time period // If received a leadership declaration: // return // Iterate over all proposal messages collected. // If a proposal message from a peer with an ID lower // than yourself was received, return. // Else, declare yourself a leader 4. 消息定义 // Leadership Message is sent during leader election to inform // remote peers about intent of peer to proclaim itself as leader message LeadershipMessage { bytes pki_id = 1; PeerTime timestamp = 2; bool is_declaration = 3; }