java - 如何为每个数据中心选择备用机器？

Question

给定的数据中心列表是 phx、slc、lvs 和机器列表、h0、h1、h2、h3，如下所述 -

Datacenters = phx, slc, lvs
Machines = h0, h1, h2, h3

我只想生成以下组合 -

a)   phx - h0
     slc - h1
     lvs - h2

b)   phx - h1
     slc - h2
     lvs - h3

c)   phx - h2
     slc - h3
     lvs - h0

d)   phx - h3
     slc - h0
     lvs - h1

我需要调用 getDatacenterMachineMapping 方法，它会给出上述结果。对于第一次调用，它应该在 coloHost 映射中给我上面的 a 结果，在第二次调用中，它应该给我上面的 b 结果在 coloHost 映射中，在第三次调用中，它应该在 coloHost 映射中给我上面的 c 结果，对于第四次调用，它应该在 coloHost map 和第五次调用中给我上面的 d 结果，它不应该给我任何东西，因为没有留下任何组合。

private static List<String> colo = Arrays.asList("phx", "slc", "lvs");
private static List<String> hosts = Arrays.asList("h0","h1","h2", "h3");

while(true) {
    Map<String, String> coloHost = getDatacenterMachineMapping();
    System.out.println(coloHost);
}

private static Map<String, String> getDatacenterMachineMapping() {

// some code here?

}

每个 channel 中的每个数据中心都应该有备用机器/主机。他们不应该得到相同的机器。例如在 a 中，如上所示 - phx 获取 h0，slc 获取 h1，lvs 获取 h2 所以所有每个数据中心的机器都不同。在第二遍中，如 b 所示 - 现在 phx 得到 h1(因为 phx 在第一遍中已经得到 h0)，slc 得到 h2 (bcoz slc 在第一遍中已经得到 h1)，并且 lvs 得到了 h3(bcoz lvs 在第一遍中已经得到了 h2)等等。

还有一个例子——如果我只有三个主机，那么下面的组合我应该只得到——

Datacenters = phx, slc, lvs
Machines = h0, h1, h2

a)   phx - h0
     slc - h1
     lvs - h2

b)   phx - h1
     slc - h2
     lvs - h0

c)   phx - h2
     slc - h0
     lvs - h1

有什么想法可以做到这一点吗？

更新:-

我试过你下面的代码，它工作正常。我在我的 main 方法中使用无限 while 循环，这意味着它会一直调用 getDatacenterMachineMapping 方法。所以这是我得到的输出，看起来不错。

{phx=h0, slc=h1, vs=h2}
{phx=h1, slc=h2, vs=h3}
{phx=h2, slc=h3, vs=h0}
{phx=h3, slc=h0, vs=h1}

{phx=h0, slc=h1, vs=h2}
{phx=h1, slc=h2, vs=h3}
{phx=h2, slc=h3, vs=h0}

因此，如果您查看上面打印出来的映射。前四个是我期望的唯一结果，之后我不希望 getDatacenterMachineMapping 给出任何结果，因为那样一次，phx 的所有四台机器都被打印出来，slc 的所有四台机器都被打印出来，vs 的所有四台机器都被打印出来。如果您看到第五行，它又开始了，我不希望 getDatacenterMachineMapping 给出结果。

下面是我试过的代码-

    public static void main(String[] args) {

        DatacenterMachineMapping dcm = new DatacenterMachineMapping(
                Arrays.asList("phx", "slc", "vs"),
                Arrays.asList("h0", "h1", "h2", "h3"));

        while(true) {
            Map<String, String> m1 = dcm.getDatacenterMachineMapping();
            System.out.println(m1);
        }
    }

    class DatacenterMachineMapping {

    private boolean firstCall = true;
    private int hostListIndex = 0;
    private List<String> datacenterList, hostList;

    public DatacenterMachineMapping(List<String> datacenterList, List<String> hostList) {
        this.datacenterList = datacenterList;
        this.hostList = hostList;
    }

    public Map<String, String> getDatacenterMachineMapping() {
        Map<String, String> datacenterMachineMapping = new HashMap<String, String>();
        if(! firstCall) {
            if(hostListIndex == 0) {
                hostListIndex = hostList.size();
            }
            hostListIndex--;
        } else {
            firstCall = false;
        }
        for(String datacenter : datacenterList) {
            if(hostListIndex == hostList.size()) {
                hostListIndex = 0;
            }
            datacenterMachineMapping.put(datacenter, hostList.get(hostListIndex++));
        }
        hostListIndex--;
        return datacenterMachineMapping;
    }
}

Answer 1

我可以从主机索引中看到的模式是，对 getDatacenterMachineMapping 的每个后续调用都从索引 i-1 开始，其中 i 是上一次调用的最后一个主机的索引。第一个调用从索引 0 开始，并围绕可用主机轮换。

例如，第一个主机列表:h0, h1, h2, h3

你有

1) 0=h0, 1=h1, 2=h2

最后一个索引是 2，从中减去 1 -> 1 这是下一次调用应该开始的索引:

2) 1=h1, 2=h2, 3=h3

现在最后一个索引是 3，即你在 2 开始下一个调用，这在列表中只剩下两个主机，然后你必须轮换，即返回索引 0 同样，这给了你

3) 2=h2, 3=h3, 0=h0

第二个主机列表也是如此。

这里是上面的示例实现(可能需要进行调整以完全符合您的要求，例如检查数据中心是否已经有任何可能的主机，您可以将其与 set 一起包装到自己的类中已分配主机的 (HashSet):

public class DatacenterMachineMapping {

    private boolean firstCall = true;
    private int hostListIndex = 0;
    private List<String> datacenterList, hostList;

    public DatacenterMachineMapping(List<String> datacenterList, List<String> hostList) {
        this.datacenterList = datacenterList;
        this.hostList = hostList;
    }

    public Map<String, String> getDatacenterMachineMapping() {
        Map<String, String> datacenterMachineMapping = new HashMap<>();
        if(! firstCall) {
            if(hostListIndex == 0) {
                hostListIndex = hostList.size();
            }
            hostListIndex--;
        } else {
            firstCall = false;
        }
        for(String datacenter : datacenterList) {
            if(hostListIndex == hostList.size()) {
                hostListIndex = 0;
            }
            datacenterMachineMapping.put(datacenter, hostList.get(hostListIndex++));
        }
        hostListIndex--;
        return datacenterMachineMapping;
    }
}

还有一些测试...

public class DatacenterMachineMappingTest {

    @Test
    public void test1() {
        DatacenterMachineMapping dcm = new DatacenterMachineMapping(
                Arrays.asList("phx", "slc", "vs"),
                Arrays.asList("h0", "h1", "h2", "h3"));

        Map<String, String> m1 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h0", m1.get("phx"));
        Assert.assertEquals("h1", m1.get("slc"));
        Assert.assertEquals("h2", m1.get("vs"));

        Map<String, String> m2 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h1", m2.get("phx"));
        Assert.assertEquals("h2", m2.get("slc"));
        Assert.assertEquals("h3", m2.get("vs"));

        Map<String, String> m3 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h2", m3.get("phx"));
        Assert.assertEquals("h3", m3.get("slc"));
        Assert.assertEquals("h0", m3.get("vs"));
    }

    @Test
    public void test2() {
        DatacenterMachineMapping dcm = new DatacenterMachineMapping(
                Arrays.asList("phx", "slc", "vs"),
                Arrays.asList("h0", "h1", "h2"));

        Map<String, String> m1 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h0", m1.get("phx"));
        Assert.assertEquals("h1", m1.get("slc"));
        Assert.assertEquals("h2", m1.get("vs"));

        Map<String, String> m2 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h1", m2.get("phx"));
        Assert.assertEquals("h2", m2.get("slc"));
        Assert.assertEquals("h0", m2.get("vs"));

        Map<String, String> m3 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h2", m3.get("phx"));
        Assert.assertEquals("h0", m3.get("slc"));
        Assert.assertEquals("h1", m3.get("vs"));
    }

    @Test
    public void test3() {
        DatacenterMachineMapping dcm = new DatacenterMachineMapping(
                Arrays.asList("phx", "slc", "vs"),
                Arrays.asList("h0", "h1"));

        Map<String, String> m1 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h0", m1.get("phx"));
        Assert.assertEquals("h1", m1.get("slc"));
        Assert.assertEquals("h0", m1.get("vs"));

        Map<String, String> m2 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h1", m2.get("phx"));
        Assert.assertEquals("h0", m2.get("slc"));
        Assert.assertEquals("h1", m2.get("vs"));

        Map<String, String> m3 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h0", m3.get("phx"));
        Assert.assertEquals("h1", m3.get("slc"));
        Assert.assertEquals("h0", m3.get("vs"));
    }

    @Test
    public void test4() {
        DatacenterMachineMapping dcm = new DatacenterMachineMapping(
                Arrays.asList("phx", "slc", "vs"),
                Arrays.asList("h0", "h1", "h2", "h3", "h4", "h5", "h6"));

        Map<String, String> m1 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h0", m1.get("phx"));
        Assert.assertEquals("h1", m1.get("slc"));
        Assert.assertEquals("h2", m1.get("vs"));

        Map<String, String> m2 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h1", m2.get("phx"));
        Assert.assertEquals("h2", m2.get("slc"));
        Assert.assertEquals("h3", m2.get("vs"));

        Map<String, String> m3 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h2", m3.get("phx"));
        Assert.assertEquals("h3", m3.get("slc"));
        Assert.assertEquals("h4", m3.get("vs"));

        Map<String, String> m4 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h3", m4.get("phx"));
        Assert.assertEquals("h4", m4.get("slc"));
        Assert.assertEquals("h5", m4.get("vs"));

        Map<String, String> m5 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h4", m5.get("phx"));
        Assert.assertEquals("h5", m5.get("slc"));
        Assert.assertEquals("h6", m5.get("vs"));

        Map<String, String> m6 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h5", m6.get("phx"));
        Assert.assertEquals("h6", m6.get("slc"));
        Assert.assertEquals("h0", m6.get("vs"));

        Map<String, String> m7 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h6", m7.get("phx"));
        Assert.assertEquals("h0", m7.get("slc"));
        Assert.assertEquals("h1", m7.get("vs"));
    }

    @Test
    public void test5() {
        DatacenterMachineMapping dcm = new DatacenterMachineMapping(
                Arrays.asList("phx", "slc", "vs", "sls"),
                Arrays.asList("h0", "h1", "h2", "h3", "h4", "h5", "h6"));

        Map<String, String> m1 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h0", m1.get("phx"));
        Assert.assertEquals("h1", m1.get("slc"));
        Assert.assertEquals("h2", m1.get("vs"));
        Assert.assertEquals("h3", m1.get("sls"));

        Map<String, String> m2 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h2", m2.get("phx"));
        Assert.assertEquals("h3", m2.get("slc"));
        Assert.assertEquals("h4", m2.get("vs"));
        Assert.assertEquals("h5", m2.get("sls"));

        Map<String, String> m3 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h4", m3.get("phx"));
        Assert.assertEquals("h5", m3.get("slc"));
        Assert.assertEquals("h6", m3.get("vs"));
        Assert.assertEquals("h0", m3.get("sls"));

        Map<String, String> m4 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h6", m4.get("phx"));
        Assert.assertEquals("h0", m4.get("slc"));
        Assert.assertEquals("h1", m4.get("vs"));
        Assert.assertEquals("h2", m4.get("sls"));

        Map<String, String> m5 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h1", m5.get("phx"));
        Assert.assertEquals("h2", m5.get("slc"));
        Assert.assertEquals("h3", m5.get("vs"));
        Assert.assertEquals("h4", m5.get("sls"));

        Map<String, String> m6 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h3", m6.get("phx"));
        Assert.assertEquals("h4", m6.get("slc"));
        Assert.assertEquals("h5", m6.get("vs"));
        Assert.assertEquals("h6", m6.get("sls"));

        Map<String, String> m7 = dcm.getDatacenterMachineMapping();
        Assert.assertEquals("h5", m7.get("phx"));
        Assert.assertEquals("h6", m7.get("slc"));
        Assert.assertEquals("h0", m7.get("vs"));
        Assert.assertEquals("h1", m7.get("sls"));
    }
}

编辑:

添加一个映射，用于映射每个数据中心及其已接收的主机:

private Map<String, Set<String>> dataCenterHostsMap = new HashMap<>();

现在添加一个将主机添加到数据中心的条件:只有在主机尚未添加时才可以添加主机:

if(addDataCenterHost(datacenter, hostList.get(hostListIndex))) {
    datacenterMachineMapping.put(datacenter, hostList.get(hostListIndex++));    
}

addDataCenterHost 方法如下所示:

private boolean addDataCenterHost(String datacenter, String host) {
    Set<String> dataCenterHostSet = dataCenterHostsMap.get(datacenter);
    if(dataCenterHostSet == null) {
        dataCenterHostSet = new HashSet<String>();
        dataCenterHostsMap.put(datacenter, dataCenterHostSet);
    }
    return dataCenterHostSet.add(host);
}

随着这个改变 test3 将不再成功运行，我想你知道为什么 ;-) 。

这里是一个更改后的 test1，用于测试第 5 次调用。

@Test
public void test1() {
    DatacenterMachineMapping dcm = new DatacenterMachineMapping(
            Arrays.asList("phx", "slc", "vs"),
            Arrays.asList("h0", "h1", "h2", "h3"));

    Map<String, String> m1 = dcm.getDatacenterMachineMapping();
    Assert.assertEquals("h0", m1.get("phx"));
    Assert.assertEquals("h1", m1.get("slc"));
    Assert.assertEquals("h2", m1.get("vs"));

    Map<String, String> m2 = dcm.getDatacenterMachineMapping();
    Assert.assertEquals("h1", m2.get("phx"));
    Assert.assertEquals("h2", m2.get("slc"));
    Assert.assertEquals("h3", m2.get("vs"));

    Map<String, String> m3 = dcm.getDatacenterMachineMapping();
    Assert.assertEquals("h2", m3.get("phx"));
    Assert.assertEquals("h3", m3.get("slc"));
    Assert.assertEquals("h0", m3.get("vs"));

    Map<String, String> m4 = dcm.getDatacenterMachineMapping();
    Assert.assertEquals("h3", m4.get("phx"));
    Assert.assertEquals("h0", m4.get("slc"));
    Assert.assertEquals("h1", m4.get("vs"));

    Map<String, String> m5 = dcm.getDatacenterMachineMapping();
    Assert.assertNull(m5.get("phx"));
    Assert.assertNull(m5.get("slc"));
    Assert.assertNull(m5.get("vs"));
}