coredns: use a TTL of 0 for our names

Containers can be be restarted with a different ip at any time so
allowing caches here doesn't make much sense given the server is local
and queries should be fast enough anyway.

Fixes #429

Signed-off-by: Paul Holzinger <[email protected]>

src/dns/coredns.rs

@@ -27,12 +27,6 @@ use std::time::Duration;
 use tokio::net::TcpListener;
 use tokio::net::UdpSocket;
 
-// Containers can be recreated with different ips quickly so
-// do not let the clients cache to dns response for to long,
-// aardvark-dns runs on the same host so caching is not that important.
-// see https://github.com/containers/netavark/discussions/644
-const CONTAINER_TTL: u32 = 60;
-
 pub struct CoreDns {
     rx: flume::Receiver<()>, // kill switch receiver
     inner: CoreDnsData,
@@ -434,7 +428,6 @@ fn reply_ptr(
                     let mut record = Record::new();
                     record
                         .set_name(Name::from_str_relaxed(name).unwrap_or_default())
-                        .set_ttl(CONTAINER_TTL)
                         .set_rr_type(RecordType::PTR)
                         .set_dns_class(DNSClass::IN)
                         .set_data(Some(RData::PTR(rdata::PTR(answer))));
@@ -481,9 +474,12 @@ fn reply_ip<'a>(
         for record_addr in resolved_ip_list {
             if let IpAddr::V4(ipv4) = record_addr {
                 let mut record = Record::new();
+                // DO NOT SET A TTL, the default is 0 which means client should not cache it.
+                // Containers can be be restarted with a different ip at any time so allowing
+                // caches here doesn't make much sense given the server is local and queries
+                // should be fast enough anyway.
                 record
                     .set_name(request_name.clone())
-                    .set_ttl(CONTAINER_TTL)
                     .set_rr_type(RecordType::A)
                     .set_dns_class(DNSClass::IN)
                     .set_data(Some(RData::A(rdata::A(ipv4))));
@@ -496,7 +492,6 @@ fn reply_ip<'a>(
                 let mut record = Record::new();
                 record
                     .set_name(request_name.clone())
-                    .set_ttl(CONTAINER_TTL)
                     .set_rr_type(RecordType::AAAA)
                     .set_dns_class(DNSClass::IN)
                     .set_data(Some(RData::AAAA(rdata::AAAA(ipv6))));

test/100-basic-name-resolution.bats

@@ -41,8 +41,9 @@ load helpers
 	gw=$(echo "$config_a1" | jq -r .network_info.podman1.subnets[0].gateway)
 	create_container "$config_a1"
 	a1_pid=$CONTAINER_NS_PID
-	run_in_container_netns "$a1_pid" "dig" "+short" "aone" "@$gw"
-	assert "$ip_a1"
+	run_in_container_netns "$a1_pid" "dig" "aone" "@$gw"
+	# check for TTL 0 here as well
+	assert "$output" =~ "aone\.[[:space:]]*0[[:space:]]*IN[[:space:]]*A[[:space:]]*$ip_a1"
 	# Set recursion bit is already set if requested so output must not
 	# contain unexpected warning.
 	assert "$output" !~ "WARNING: recursion requested but not available"

test/500-reverse-lookups.bats

@@ -29,15 +29,15 @@ load helpers
 	dig_reverse "$a1_pid" "$a2_ip" "$gw"
 	echo -e "Output:\n${output}\n"
 	a2_expected_name=$(echo $a2_ip | awk -F. '{printf "%d.%d.%d.%d.in-addr.arpa.", $4, $3, $2, $1}')
-	assert "$output" =~ "$a2_expected_name[ 	].*[ 	]atwo\."
-	assert "$output" =~ "$a2_expected_name[ 	].*[ 	]a2\."
-	assert "$output" =~ "$a2_expected_name[ 	].*[ 	]2a\."
+	assert "$output" =~ "$a2_expected_name[[:space:]]*0[[:space:]]*IN[[:space:]]*PTR[[:space:]]*atwo\."
+	assert "$output" =~ "$a2_expected_name[[:space:]]*0[[:space:]]*IN[[:space:]]*PTR[[:space:]]*a2\."
+	assert "$output" =~ "$a2_expected_name[[:space:]]*0[[:space:]]*IN[[:space:]]*PTR[[:space:]]*2a\."
 	dig_reverse "$a2_pid" "$a1_ip" "$gw"
 	echo -e "Output:\n${output}\n"
 	a1_expected_name=$(echo $a1_ip | awk -F. '{printf "%d.%d.%d.%d.in-addr.arpa.", $4, $3, $2, $1}')
-	assert "$output" =~ "$a1_expected_name[ 	].*[ 	]aone\."
-	assert "$output" =~ "$a1_expected_name[ 	].*[ 	]a1\."
-	assert "$output" =~ "$a1_expected_name[ 	].*[ 	]1a\."
+	assert "$output" =~ "$a1_expected_name[[:space:]]*0[[:space:]]*IN[[:space:]]*PTR[[:space:]]*aone\."
+	assert "$output" =~ "$a1_expected_name[[:space:]]*0[[:space:]]*IN[[:space:]]*PTR[[:space:]]*a1\."
+	assert "$output" =~ "$a1_expected_name[[:space:]]*0[[:space:]]*IN[[:space:]]*PTR[[:space:]]*1a\."
 }
 
 @test "check reverse lookups on ipaddress v6" {