HTTPClient doesn't respect CNAME TTL

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Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• If there is a stack dump, I have decoded it.
• I have filled out all fields below.

Platform

• Hardware: ESP8266
• Core Version: ??? Arduino IDE 2.3.2 2024-02-20T09:54:08669Z ???
• Development Env: Arduino IDE
• Operating System: Debian 11

Settings in IDE

• Module: Wemos D1 mini (clone)
• Flash Mode: ???
• Flash Size: ???
• lwip Variant: ???
• Reset Method: ???
• Flash Frequency: ???
• CPU Frequency: ???
• Upload Using: Serial
• Upload Speed: 921600

Problem Description

I am sending web requests to systems which are configured for failover using CNAME records with low TTL values which point to A records with higher values. For example, I have 4 DNS records:

• myproject.example.com CNAME TTL 60 -> node1.example.com (primary)
• myproject.example.com CNAME TTL 60 -> node2.example.com (secondary)
• node1.example.com A TTL 86400 203.0.113.1
• node2.example.com A TTL 86400 198.51.100.2

I am expecting the TTL of both records to be respected. When the CNAME expires a new lookup should be performed.

In practice, the esp8266 library appears to ignore the CNAME TTL and a new lookup is performed only when the underlying A record expires.

Sketch

#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>

void setup() {
  WiFi.begin("TheSSID", "ThePSK");
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print('.');
  }
}

void webRequest() {
  WiFiClient client;
  HTTPClient http;
  if (http.begin(client, "http://myproject.example.com/useful_endpoint/")) {
    int httpCode = http.GET();
    if (httpCode > 0) {
        Serial.printf("[HTTPS] GET status code: %d\n", httpCode);
    } else {
        Serial.printf("[HTTPS] GET failed; status code: %d)\n", httpCode);
    }
    http.end();
  } else {
    Serial.print("connection failed");
  }
}

void loop() {
  delay(5000);
  webRequest();
}