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https://github.com/taigrr/nats.docs
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120 lines
3.0 KiB
Markdown
120 lines
3.0 KiB
Markdown
# Avoiding the Thundering Herd
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When a server goes down, there is a possible anti-pattern called the _Thundering Herd_ where all of the clients try to reconnect immediately, thus creating a denial of service attack. In order to prevent this, most NATS client libraries randomize the servers they attempt to connect to. This setting has no effect if only a single server is used, but in the case of a cluster, randomization, or shuffling, will ensure that no one server bears the brunt of the client reconnect attempts.
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However, if you want to disable the randomization process for connect and re-connect, so that servers are always checked in the same order, you can do that in most libraries with a connection option:
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{% tabs %}
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{% tab title="Go" %}
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```go
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servers := []string{"nats://127.0.0.1:1222",
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"nats://127.0.0.1:1223",
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"nats://127.0.0.1:1224",
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}
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nc, err := nats.Connect(strings.Join(servers, ","), nats.DontRandomize())
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if err != nil {
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log.Fatal(err)
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}
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defer nc.Close()
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// Do something with the connection
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```
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{% endtab %}
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{% tab title="Java" %}
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```java
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Options options = new Options.Builder().
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server("nats://demo.nats.io:4222").
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noRandomize(). // Disable reconnect shuffle
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build();
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Connection nc = Nats.connect(options);
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// Do something with the connection
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nc.close();
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```
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{% endtab %}
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{% tab title="JavaScript" %}
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```javascript
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let nc = NATS.connect({
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noRandomize: true,
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servers: [
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"nats://127.0.0.1:4443",
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"nats://demo.nats.io:4222"
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]
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});
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```
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{% endtab %}
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{% tab title="Python" %}
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```python
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nc = NATS()
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await nc.connect(
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servers=[
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"nats://demo.nats.io:1222",
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"nats://demo.nats.io:1223",
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"nats://demo.nats.io:1224"
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],
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dont_randomize=True,
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)
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# Do something with the connection
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await nc.close()
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```
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{% endtab %}
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{% tab title="Ruby" %}
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```ruby
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require 'nats/client'
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NATS.start(servers: ["nats://127.0.0.1:1222", "nats://127.0.0.1:1223", "nats://127.0.0.1:1224"], dont_randomize_servers: true) do |nc|
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# Do something with the connection
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# Close the connection
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nc.close
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end
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```
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{% endtab %}
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{% tab title="TypeScript" %}
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```typescript
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// will throw an exception if connection fails
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let nc = await connect({
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noRandomize: true,
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servers: [
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"nats://127.0.0.1:4443",
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"nats://demo.nats.io:4222"
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]
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});
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nc.close();
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```
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{% endtab %}
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{% tab title="C" %}
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```c
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natsConnection *conn = NULL;
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natsOptions *opts = NULL;
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natsStatus s = NATS_OK;
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const char *servers[] = {"nats://127.0.0.1:1222", "nats://127.0.0.1:1223", "nats://127.0.0.1:1224"};
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s = natsOptions_Create(&opts);
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if (s == NATS_OK)
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s = natsOptions_SetServers(opts, servers, 3);
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if (s == NATS_OK)
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s = natsOptions_SetNoRandomize(opts, true);
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if (s == NATS_OK)
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s = natsConnection_Connect(&conn, opts);
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(...)
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// Destroy objects that were created
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natsConnection_Destroy(conn);
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natsOptions_Destroy(opts);
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```
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{% endtab %}
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{% endtabs %}
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