k8s其实太复杂，对于小团队来说，光是hold住k8s就要花好几个人力，而且k8s更新迭代太快了，有种上了贼船就下不来的感觉。 nomad就简单多了，就是一个调度器，啥也不带，显得有点简陋，不过，对于中小型团队来说，完全足够。
下面是 k8s 和 nomad 的简单对比：
| 对比项 | k8s | nomad |
|---|---|---|
| 简单易用 | 复杂 | 简单 |
| 概念复杂度 | 复杂 | 中等 |
| 更新迭代速度 | 太快了 | 合理 |
| 安装复杂度 | 复杂 | 简单 |
| 功能丰富程度 | 丰富 | 简单 |
安装之前要了解一些术语：https://www.nomadproject.io/docs/internals/architecture.html
wget https://releases.hashicorp.com/nomad/0.9.1/nomad_0.9.1_linux_amd64.zip/usr/local/bin 下sudo chown root:root /usr/local/bin/nomad编辑 /etc/systemd/system/nomad.service，内容是：
[Unit]
Description=Nomad
Documentation=https://nomadproject.io/docs/
Wants=network-online.target
After=network-online.target
# When using Nomad with Consul it is not necessary to start Consul first. These
# lines start Consul before Nomad as an optimization to avoid Nomad logging
# that Consul is unavailable at startup.
#Wants=consul.service
#After=consul.service
[Service]
ExecReload=/bin/kill -HUP $MAINPID
ExecStart=/usr/local/bin/nomad agent -config /etc/nomad.d
KillMode=process
KillSignal=SIGINT
LimitNOFILE=infinity
LimitNPROC=infinity
Restart=on-failure
RestartSec=2
StartLimitBurst=3
StartLimitIntervalSec=10
TasksMax=infinity
[Install]
WantedBy=multi-user.target
创建nomad用于存储数据用的文件夹 sudo mkdir -p /opt/nomad/
创建nomad用于存储配置用的文件夹 sudo mkdir -p /etc/nomad.d/
创建公共配置，路径是 /etc/nomad.d/nomad.hcl，内容是：
datacenter就是一个数据中心，data_dir就是刚才我们创建的nomad存储数据用的
datacenter = "home"
data_dir = "/opt/nomad"
/etc/nomad.d/server.hcl，内容是：server_join 里把我们的三个节点都加进去。也可以只加自己，之后用命令来加
server {
enabled = true
bootstrap_expect = 3
server_join {
retry_join = ["192.168.122.116:4648", "192.168.122.221:4648", "192.168.122.20:4648"]
}
}
把上面的步骤改成一个脚本，每台机器上执行一下即可：
#!/bin/bash
sudo chown root:root /usr/local/bin/nomad
cat > /etc/systemd/system/nomad.service << EOF
[Unit]
Description=Nomad
Documentation=https://nomadproject.io/docs/
Wants=network-online.target
After=network-online.target
# When using Nomad with Consul it is not necessary to start Consul first. These
# lines start Consul before Nomad as an optimization to avoid Nomad logging
# that Consul is unavailable at startup.
#Wants=consul.service
#After=consul.service
[Service]
ExecReload=/bin/kill -HUP $MAINPID
ExecStart=/usr/local/bin/nomad agent -config /etc/nomad.d
KillMode=process
KillSignal=SIGINT
LimitNOFILE=infinity
LimitNPROC=infinity
Restart=on-failure
RestartSec=2
StartLimitBurst=3
StartLimitIntervalSec=10
TasksMax=infinity
[Install]
WantedBy=multi-user.target
EOF
sudo mkdir -p /opt/nomad/
sudo mkdir -p /etc/nomad.d/
cat > /etc/nomad.d/nomad.hcl << EOF
datacenter = "home"
data_dir = "/opt/nomad"
EOF
cat > /etc/nomad.d/server.hcl << EOF
server {
enabled = true
bootstrap_expect = 5
server_join {
retry_join = ["192.168.122.116:4648", "192.168.122.221:4648", "192.168.122.20:4648"]
}
}
EOF
/etc/nomad.d/client.hcl，内容是：把server地址写进去，写一个即可，因为他们会同步的
client {
enabled = true
servers = ["192.168.122.116:4647"]
}
注意，要先创建好这些，然后再启动nomad。不能启动之后，再复制虚拟机。如果这样干的话，就会发现，
nomad server members有输出，但是nomad node status却只有一个。解决方案是把nomad停止服务，把/opt/nomad的数据删掉，再把 nomad 重新启动。
启动之后，就发现搭好了，这比 k8s 简单了几个数量级啊：
jiajun@ubuntu1:~$ nomad server members
Name Address Port Status Leader Protocol Build Datacenter Region
ubuntu1.global 192.168.122.116 4648 alive true 2 0.9.1 home global
ubuntu2.global 192.168.122.221 4648 alive false 2 0.9.1 home global
ubuntu3.global 192.168.122.20 4648 alive false 2 0.9.1 home global
jiajun@ubuntu1:~$ nomad node status
ID DC Name Class Drain Eligibility Status
1e1a0cb2 home ubuntu3 <none> false eligible ready
3afa1c4e home ubuntu2 <none> false eligible ready
880defee home ubuntu1 <none> false eligible ready
如果发现死都选不出leader，那么重来一遍即可。
终于搭好了一个nomad集群，然后跑一个job：
job "httpecho" {
region = "global"
datacenters = ["home"]
type = "service"
group "web" {
count = 2
task "server" {
driver = "docker"
config {
image = "hashicorp/http-echo"
args = ["-text", "hello world"]
port_map = {
http = 5678
}
}
resources {
network {
mbits = 250
port "http" {}
}
}
}
}
}
执行一下：
jiajun@ubuntu1:~$ nomad job run httpecho.nomad
==> Monitoring evaluation "ef18e4d2"
Evaluation triggered by job "httpecho"
Allocation "20515739" created: node "1e1a0cb2", group "web"
Allocation "bfa03c3c" created: node "3afa1c4e", group "web"
Evaluation status changed: "pending" -> "complete"
==> Evaluation "ef18e4d2" finished with status "complete"
jiajun@ubuntu1:~$ logout
Connection to 192.168.122.116 closed.
jiajun@idea ~ $ ansible ubuntu -a 'docker ps -a'
ubuntu3 | CHANGED | rc=0 >>
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
e0c56865dd11 hashicorp/http-echo "/http-echo -text 'h…" 5 seconds ago Up 5 seconds 192.168.122.20:27191->5678/tcp, 192.168.122.20:27191->5678/udp server-20515739-01f9-e7d4-ffff-07b4c64df802
ubuntu2 | CHANGED | rc=0 >>
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
0c3c7a9ad015 hashicorp/http-echo "/http-echo -text 'h…" 7 seconds ago Up 6 seconds 192.168.122.221:21704->5678/tcp, 192.168.122.221:21704->5678/udp server-bfa03c3c-64f3-ca87-4b28-e157ea980181
ubuntu1 | CHANGED | rc=0 >>
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
jiajun@idea ~ $ http 192.168.122.221:21704
HTTP/1.1 200 OK
Content-Length: 12
Content-Type: text/plain; charset=utf-8
Date: Fri, 31 May 2019 06:34:49 GMT
X-App-Name: http-echo
X-App-Version: 0.2.3
hello world
大功告成！
初步体验下来，nomad比k8s易用性上简直好太多，但是有一个阻碍中大型团队使用的问题：开源版本木有namespace支持。。。可惜啊可惜， 眼看容器调度的天下都要被k8s吃完了，还不快放开功能来抢一抢份额。
参考资料：
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