DNS Upstream TTL troubles

[gfw-killer]

Hello
Some domains like Instagram domains have TTL like 5 seconds, and as after #4526 Xray uses the upstream TTL, it made some Apps like Instagram laggy and the overall Xray client user-experience lower, and also made servers to use more CPU because they must repeatedly resolve domains with low TTL
To fix it we need a min-ttl option to increase TTL when it's lower than N seconds
I know it's possible to use an external DNS resolver for Server, but for Xray Clients we need it
Could you guys help please? @Meo597 @patterniha @Fangliding
Thanks

[Fangliding]

我记得之前不是有一个最低ttl的吗

[patterniha]

TTL changes in a rotating manner:

60, 59, ..., 2, 1, 60, 59, ... , 2, 1, 60, .......

If you saw ttl=5, if you try 5 seconds later, you see ttl=60 this time.

So the average-interval between requests will be at least 60 seconds, and there is no problem.

(Instagram domains ttl is 60 to 1)

[Meo597]

返回真实ttl是为了避免特定场景下因过久的cache导致目标域名解析到了已废弃ip的问题
比如公有云k8s弹性收缩、比如ddns
这是为了让xray行为和网站管理员预期一致

以前是返回给客户端的ttl永远为600，因此你可能十分钟感受到一次卡顿，把问题掩盖住了

但增加CPU负载我表示不太理解，没遇到过，你有数据吗

在“强制改写ttl”出来之前，你可以用这种办法缓解：

• 如果你是透明代理，改用fakeip

• 如果你是非透明代理，则：

  1. xray客户端入站出开sniff+overrideDest，把IP改写为域名
  2. 路由domainStrategy=AsIs
     or IPIfNonMatch
     or 把IP规则放前，域名规则放后，设为IPOnDemand

由于你的客户端和服务器之间的连接质量不佳，实际上你应该永远使用这种办法

[gfw-killer]

TTL changes in a rotating manner:

60, 59, ..., 2, 1, 60, 59, ... , 2, 1, 60, .......

If you saw ttl=5, if you try 5 seconds later, you see ttl=60 this time.

you are right, so the problem is that Xray server does not adjust ttl based on client request, for example when dns ttl in Xray server cache have 5 seconds to expire and client sends dns request to xray server, xray server will send ttl 5 to the client, and client must 5 seconds later resolve the same domain again to get ttl 60
and no website is going to change IP every minute, if there was such option, i would change the min-ttl of client to 1 min to never get a low ttl, and change server min-rtt to 5 minutes to not get banned by remote DNS servers

[Meo597]

或许可以有个当 PC/Phone 向 Xray 内置的 DNS请求 时检查 TTL < 10
主动刷新缓存
@patterniha

[patterniha]

Maybe there could be a way to check TTL < 10 when the PC/Phone makes a DNS request to Xray's built-in DNS and then actively refresh the cache. @patterniha

There is no difference in practice.

Even if you don't use xray-core, the ttl bevave in rotatating manner.

Xray-core just pass the received ttl.

So even you don't use vpn or xray-core, you may received 5 seconds ttl.

But this is one time, and the average-interval between requests is at least 60 seconds.

///

So Xray-core-dns has no problem and this issue can be closed.

[Fangliding]

查询一次DNS并没有很大开销 哪怕ttl全是1也只是让xray变成disableCache 把每次dns请求都转发出去而已 所以我并不觉得这是个问题 顶多是有人希望可以refine一下不太想见到的ttl=1