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Merge pull request etcd-io#582 from benbjohnson/proxy
Proxies & Config API
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| ## Proxies | ||
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| Adding peers in an etcd cluster adds network, CPU, and disk overhead to the leader since each one requires replication. | ||
| Peers primarily provide resiliency in the event of a leader failure but the benefit of more failover nodes decreases as the cluster size increases. | ||
| A lightweight alternative is the proxy. | ||
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| Proxies are a way for an etcd node to forward requests along to the cluster but the proxies are not part of the Raft cluster themselves. | ||
| This provides an easier API for local applications while reducing the overhead required by a regular peer node. | ||
| Proxies also act as standby nodes in the event that a peer node in the cluster has not recovered after a long duration. | ||
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| ## Configuration Parameters | ||
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| Proxies require two additional configuration parameters: active size & promotion delay. | ||
| The active size specifies a target size for the number of peers in the cluster. | ||
| If there are not enough peers to meet the active size then proxies are promoted to peers until the peer count is equal to the active size. | ||
| If there are more peers than the target active size then peers are demoted to proxies. | ||
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| The promotion delay specifies how long the cluster should wait before removing a dead peer and promoting a proxy. | ||
| By default this is 30 minutes. | ||
| If a peer is inactive for 30 minutes then the peer is removed and a live proxy is found to take its place. | ||
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| ## Logical Workflow | ||
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| Start a etcd machine and join the cluster: | ||
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| ``` | ||
| If peer count less than active size: | ||
| If machine already exists as a proxy: | ||
| Remove machine from proxy list | ||
| Join as peer | ||
| If peer count greater than or equal to active size: | ||
| Join as proxy | ||
| ``` | ||
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| Remove an existing etcd machine from the cluster: | ||
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| ``` | ||
| If machine exists in peer list: | ||
| Remove from peer list | ||
| If machine exists in proxy list: | ||
| Remove from proxy list | ||
| ``` | ||
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| Leader's active size monitor: | ||
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| ``` | ||
| Loop: | ||
| Sleep 5 seconds | ||
| If peer count less than active size: | ||
| If proxy count greater than zero: | ||
| Request a random proxy to rejoin | ||
| Goto Loop | ||
| If peer count greater than active size: | ||
| Demote randomly selected peer | ||
| Goto Loop | ||
| ``` | ||
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| Leader's peer activity monitor: | ||
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| ``` | ||
| Loop: | ||
| Sleep 5 seconds | ||
| For each peer: | ||
| If peer last activity time greater than promote delay: | ||
| Demote peer | ||
| Goto Loop | ||
| ``` |
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| @@ -0,0 +1,39 @@ | ||
| package server | ||
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| import ( | ||
| "time" | ||
| ) | ||
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| const ( | ||
| // DefaultActiveSize is the default number of active followers allowed. | ||
| DefaultActiveSize = 9 | ||
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| // MinActiveSize is the minimum active size allowed. | ||
| MinActiveSize = 3 | ||
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| // DefaultPromoteDelay is the default elapsed time before promotion. | ||
| DefaultPromoteDelay = int((30 * time.Minute) / time.Second) | ||
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| // MinPromoteDelay is the minimum promote delay allowed. | ||
| MinPromoteDelay = int((2 * time.Second) / time.Second) | ||
| ) | ||
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| // ClusterConfig represents cluster-wide configuration settings. | ||
| // These settings can only be changed through Raft. | ||
| type ClusterConfig struct { | ||
| // ActiveSize is the maximum number of node that can join as Raft followers. | ||
| // Nodes that join the cluster after the limit is reached are proxies. | ||
| ActiveSize int `json:"activeSize"` | ||
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| // PromoteDelay is the amount of time, in seconds, after a node is | ||
| // unreachable that it will be swapped out for a proxy node, if available. | ||
| PromoteDelay int `json:"promoteDelay"` | ||
| } | ||
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| // NewClusterConfig returns a cluster configuration with default settings. | ||
| func NewClusterConfig() *ClusterConfig { | ||
| return &ClusterConfig{ | ||
| ActiveSize: DefaultActiveSize, | ||
| PromoteDelay: DefaultPromoteDelay, | ||
| } | ||
| } |
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| package server | ||
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| import ( | ||
| "fmt" | ||
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| "github.com/coreos/etcd/log" | ||
| "github.com/coreos/etcd/third_party/github.com/goraft/raft" | ||
| ) | ||
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| func init() { | ||
| raft.RegisterCommand(&DemoteCommand{}) | ||
| } | ||
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| // DemoteCommand represents a command to change a peer to a proxy. | ||
| type DemoteCommand struct { | ||
| Name string `json:"name"` | ||
| } | ||
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| // CommandName returns the name of the command. | ||
| func (c *DemoteCommand) CommandName() string { | ||
| return "etcd:demote" | ||
| } | ||
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| // Apply executes the command. | ||
| func (c *DemoteCommand) Apply(context raft.Context) (interface{}, error) { | ||
| ps, _ := context.Server().Context().(*PeerServer) | ||
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| // Ignore this command if there is no peer. | ||
| if !ps.registry.PeerExists(c.Name) { | ||
| return nil, fmt.Errorf("peer does not exist: %s", c.Name) | ||
| } | ||
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| // Save URLs. | ||
| clientURL, _ := ps.registry.ClientURL(c.Name) | ||
| peerURL, _ := ps.registry.PeerURL(c.Name) | ||
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| // Remove node from the shared registry. | ||
| err := ps.registry.UnregisterPeer(c.Name) | ||
| if err != nil { | ||
| log.Debugf("Demote peer %s: Error while unregistering (%v)", c.Name, err) | ||
| return nil, err | ||
| } | ||
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| // Delete from stats | ||
| delete(ps.followersStats.Followers, c.Name) | ||
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| // Remove peer in raft | ||
| err = context.Server().RemovePeer(c.Name) | ||
| if err != nil { | ||
| log.Debugf("Demote peer %s: (%v)", c.Name, err) | ||
| return nil, err | ||
| } | ||
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| // Register node as a proxy. | ||
| ps.registry.RegisterProxy(c.Name, peerURL, clientURL) | ||
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| // Update mode if this change applies to this server. | ||
| if c.Name == ps.Config.Name { | ||
| log.Infof("Demote peer %s: Set mode to proxy with %s", c.Name, ps.server.Leader()) | ||
| ps.proxyPeerURL, _ = ps.registry.PeerURL(ps.server.Leader()) | ||
| go ps.setMode(ProxyMode) | ||
| } | ||
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| return nil, nil | ||
| } | ||
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| // NodeName returns the name of the affected node. | ||
| func (c *DemoteCommand) NodeName() string { | ||
| return c.Name | ||
| } |
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