Se alguém se importa, resolvi o problema com
sysctl -w net.ipv4.conf.docker0.route_localnet=1
Eu tenho um host (A) com um daemon StatsD ouvindo em 127.0.0.1:8125:
root@A# netstat -uln
Proto Recv-Q Send-Q Local Address Foreign Address State
udp 0 0 127.0.0.1:8125 0.0.0.0:*
E um contêiner docker (B) iniciado no host A, com rede de ponte:
root@A# docker network inspect bridge
[
{
"Name": "bridge",
"Id": "02b013615710b375744975ff74bdd0b5dcc8c25debba4fa23ad8f53da2c684e3",
"Created": "2017-04-21T08:13:04.389253904Z",
"Scope": "local",
"Driver": "bridge",
"EnableIPv6": false,
"IPAM": {
"Driver": "default",
"Options": null,
"Config": [
{
"Subnet": "172.17.0.0/16",
"Gateway": "172.17.0.1"
}
]
},
"Internal": false,
"Attachable": false,
"Containers": {
"e1fde895c871504f64627c88531a380269ee9fe8a9fa5237a98c81500fa47a7a": {
"Name": "B",
"EndpointID": "4e4a8758e811bb48cecec67d339c182c60e1d955126506cddb7d451e818c5535",
"MacAddress": "02:42:ac:11:00:02",
"IPv4Address": "172.17.0.2/16",
"IPv6Address": ""
}
},
"Options": {
"com.docker.network.bridge.default_bridge": "true",
"com.docker.network.bridge.enable_icc": "true",
"com.docker.network.bridge.enable_ip_masquerade": "true",
"com.docker.network.bridge.host_binding_ipv4": "0.0.0.0",
"com.docker.network.bridge.name": "docker0",
"com.docker.network.driver.mtu": "1500"
},
"Labels": {}
}
]
Minhas interfaces de rede:
root@A# ip addr show
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
inet 127.0.0.1/8 scope host lo
valid_lft forever preferred_lft forever
inet6 ::1/128 scope host
valid_lft forever preferred_lft forever
4: docker0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue state UP group default
link/ether 02:42:60:00:2c:63 brd ff:ff:ff:ff:ff:ff
inet 172.17.0.1/16 scope global docker0
valid_lft forever preferred_lft forever
inet6 fe80::42:60ff:fe00:2c63/64 scope link
valid_lft forever preferred_lft forever
Agora quero enviar pacotes UDP com métricas do contêiner B para o StatsD em A (127.0.0.1:8125), algo assim:
root@B# echo "metric.name:1|c" | nc -w 1 -u 172.17.0.1 8125
O que devo fazer para encaminhar os pacotes UDP de 172.17.0.1:8125 para 127.0.0.1:8125?
Eu tentei adicionar a regra iptables:
root@A# iptables -t nat -A PREROUTING -p udp -i docker0 -d 172.17.0.1 --dport 8125 -j DNAT --to-destination 127.0.0.1:8125
Mas ainda não vejo meus pacotes UDP no StatsD.
iptables nat:
root@A# iptables -t nat -L -n -v
Chain PREROUTING (policy ACCEPT 736 packets, 53956 bytes)
pkts bytes target prot opt in out source destination
211K 13M DOCKER all -- * * 0.0.0.0/0 0.0.0.0/0 ADDRTYPE match dst-type LOCAL
3 116 DNAT udp -- docker0 * 0.0.0.0/0 172.17.0.1 udp dpt:8125 to:127.0.0.1:8125
Chain INPUT (policy ACCEPT 724 packets, 53227 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 838 packets, 57674 bytes)
pkts bytes target prot opt in out source destination
20 1186 DOCKER all -- * * 0.0.0.0/0 !127.0.0.0/8 ADDRTYPE match dst-type LOCAL
Chain POSTROUTING (policy ACCEPT 1407 packets, 91792 bytes)
pkts bytes target prot opt in out source destination
84593 5296K MASQUERADE all -- * !docker0 172.17.0.0/16 0.0.0.0/0
0 0 MASQUERADE tcp -- * * 172.17.0.2 172.17.0.2 tcp dpt:8080
Chain DOCKER (2 references)
pkts bytes target prot opt in out source destination
1285 77084 RETURN all -- docker0 * 0.0.0.0/0 0.0.0.0/0
933 55820 DNAT tcp -- !docker0 * 0.0.0.0/0 0.0.0.0/0 tcp dpt:80 to:172.17.0.2:8080
Filtro iptables:
root@A# iptables -t filter -L -n -v
Chain INPUT (policy ACCEPT 33641 packets, 5895K bytes)
pkts bytes target prot opt in out source destination
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
2298K 1931M DOCKER-ISOLATION all -- * * 0.0.0.0/0 0.0.0.0/0
1165K 662M DOCKER all -- * docker0 0.0.0.0/0 0.0.0.0/0
602K 560M ACCEPT all -- * docker0 0.0.0.0/0 0.0.0.0/0 ctstate RELATED,ESTABLISHED
1133K 1269M ACCEPT all -- docker0 !docker0 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT all -- docker0 docker0 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT 27954 packets, 14M bytes)
pkts bytes target prot opt in out source destination
Chain DOCKER (1 references)
pkts bytes target prot opt in out source destination
8285 685K ACCEPT tcp -- !docker0 docker0 0.0.0.0/0 172.17.0.2 tcp dpt:8080
Chain DOCKER-ISOLATION (1 references)
pkts bytes target prot opt in out source destination
2298K 1931M RETURN all -- * * 0.0.0.0/0 0.0.0.0/0
O que está errado?
Importante:
Se alguém se importa, resolvi o problema com
sysctl -w net.ipv4.conf.docker0.route_localnet=1