:::success <font size=6> serf </font> ::: [TOC] # About serf 官網 https://www.serf.io/ GitHub https://github.com/hashicorp/serf What is Serf? > from https://www.serf.io/intro/index.html > Serf is a tool for cluster membership, failure detection, and orchestration that is decentralized, fault-tolerant and highly available. Serf runs on every major platform: Linux, Mac OS X, and Windows. It is extremely lightweight: it uses 5 to 10 MB of resident memory and primarily communicates using infrequent UDP messages. # Command Usage ``` Usage: serf [--version] [--help] <command> [<args>] Available commands are: agent Runs a Serf agent event Send a custom event through the Serf cluster force-leave Forces a member of the cluster to enter the "left" state info Provides debugging information for operators join Tell Serf agent to join cluster keygen Generates a new encryption key keys Manipulate the internal encryption keyring used by Serf leave Gracefully leaves the Serf cluster and shuts down members Lists the members of a Serf cluster monitor Stream logs from a Serf agent query Send a query to the Serf cluster reachability Test network reachability rtt Estimates network round trip time between nodes tags Modify tags of a running Serf agent version Prints the Serf version ``` # Demo 準備兩台電腦 * A 電腦, esvm-win10 , ip: 172.22.12.27 * B 電腦, esvm-agwin , ip: 172.22.12.238 A 電腦執行 ```shell= $ serf agent ``` B 電腦執行 ```shell= $ serf agent ``` A 電腦新開另一個視窗執行 ```shell= $ serf join 172.22.12.238 ``` A 電腦、B 電腦此時各自時執行 serf members, 都可以看到 cluster 裡有兩個成員 ``` $ serf members esvm-win10 172.22.12.27:7946 alive esvm-agwin 172.22.12.238:7946 alive ``` A 電腦發送 custom event ``` $ serf event hello-world Event 'hello-world' dispatched! Coalescing enabled: true ``` 此時 A 電腦跟 B 電腦的 agent，都會出現以下訊息 ``` 2022/05/13 13:55:59 [INFO] agent: Received event: user-event: hello-world ``` # Event Types of Events * member-join - One or more members have joined the cluster. * member-leave - One or more members have gracefully left the cluster. * member-failed - One or more members have failed, meaning that they didn't properly respond to ping requests. * member-update - One or more members have updated, likely to update the associated tags * member-reap - Serf has removed one or more members from its list of members. This means a failed node exceeded the * reconnect_timeout, or a left node reached the tombstone_timeout. * user - A custom user event, covered later in this guide. * query - A query event, covered later in this guide # Event Handler ```bash= #!/bin/bash echo echo "New event: ${SERF_EVENT}. Data follows..." while read line; do printf "${line}\n" done ```