Keepalive property for the connection between client and elasticsearch should be considered as configurable. Futher more, i do think it's good to keep it alive by default.

Here is the issue:

When read/write elasticsearch in high concurrency, threads have chances to stuck on obsolete connection between client and elasticsearch. The more threads involves, the quicker stucking on connection happens. The reason is described here:

Worse, if the connection is dropped silently while a request is in flight then the client may block indefinitely since it will send no more data on this connection and will therefore never find out that it's been closed.

And here is the situation i run into. Logs can also be found here: - https://stackoverflow.com/questions/73217318/elasticsearch-java-response-stuck

similar issue: - https://github.com/elastic/elasticsearch/issues/65909

However, spring boot can't config keepalive through current properties. We have to write some config codes like:

    @Bean
    public RestClientBuilderCustomizer keepalive() {
        return new RestClientBuilderCustomizer() {
            @Override
            public void customize(RestClientBuilder builder) {

            }

            @Override
            public void customize(HttpAsyncClientBuilder builder) {
                builder.setDefaultIOReactorConfig(IOReactorConfig.custom().setSoKeepAlive(true).build());
                log.info("es tcp keep-alive must be enabled!");
            }
        };
    }

So i add some support for spring.elasticsearch.keepalive=true to make it easier to config.

Comment From: pivotal-cla

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Comment From: pivotal-cla

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Comment From: snicoll

@puppylpg thank you for making your first contribution to Spring Boot.

Comment From: puppylpg

Will this mr be merged into 2.x.x besides 3.0.0-M5?

Comment From: wilkinsona

Sorry, it won't. It's an enhancement so it only belongs in a new major or minor release. We don't have any plans at the moment for a 2.8 release so 3.0 is the next available release in which it can be included.

Comment From: puppylpg

ok, thanks for your reply (sad, for still using jdk8 in our production environment :sweat_smile::sweat_smile::sweat_smile:)