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问题:
I am developing a service and using there docker compose to spin services like postgres, redis, elasticsearch. I have a web application that is based on RubyOnRails and writes and reads from all those services.
Here is my docker-compose.yml
version: '2' services: redis: image: redis:2.8 networks: - frontapp elasticsearch: image: elasticsearch:2.2 networks: - frontapp postgres: image: postgres:9.5 environment: POSTGRES_USER: elephant POSTGRES_PASSWORD: smarty_pants POSTGRES_DB: elephant volumes: - /var/lib/postgresql/data networks: - frontapp networks: frontapp: driver: bridge
And i can ping containers within this network
$ docker-compose run redis /bin/bash root@777501e06c03:/data# ping postgres PING postgres (172.20.0.2): 56 data bytes 64 bytes from 172.20.0.2: icmp_seq=0 ttl=64 time=0.346 ms 64 bytes from 172.20.0.2: icmp_seq=1 ttl=64 time=0.047 ms ...
So far so good. Now I want to run ruby on rails application on my host machine but be able to access postgres instance with url like postgresql://username:password@postgres/database currently that is not possible
$ ping postgres ping: unknown host postgres
I can see my network in docker
$ docker network ls NETWORK ID NAME DRIVER ac394b85ce09 bridge bridge 0189d7e86b33 elephant_default bridge 7e00c70bde3b elephant_frontapp bridge a648554a72fa host host 4ad9f0f41b36 none null
And I can see an interface to it
$ ifconfig br-0189d7e86b33 Link encap:Ethernet HWaddr 02:42:76:72:bb:c2 inet addr:172.18.0.1 Bcast:0.0.0.0 Mask:255.255.0.0 inet6 addr: fe80::42:76ff:fe72:bbc2/64 Scope:Link UP BROADCAST MULTICAST MTU:1500 Metric:1 RX packets:36 errors:0 dropped:0 overruns:0 frame:0 TX packets:60 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:2000 (2.0 KB) TX bytes:8792 (8.7 KB) br-7e00c70bde3b Link encap:Ethernet HWaddr 02:42:e7:d1:fe:29 inet addr:172.20.0.1 Bcast:0.0.0.0 Mask:255.255.0.0 inet6 addr: fe80::42:e7ff:fed1:fe29/64 Scope:Link UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1 RX packets:1584 errors:0 dropped:0 overruns:0 frame:0 TX packets:1597 errors:0 dropped:0 overruns:0 carrier:0 collisions:0 txqueuelen:0 RX bytes:407137 (407.1 KB) TX bytes:292299 (292.2 KB) ...
But i am not sure what should I do next. I tried to play a bit with /etc/resolv.conf, mainly with nameserver directive, but that had no effect.
I would appreciate any help of suggestions how to configure this setup correctly.
UPDATE
After browsing through Internet resources I managed to assign static IP addresses to boxes. For now it is enough for me to continue development. Here is my current docker-compose.yml
version: '2' services: redis: image: redis:2.8 networks: frontapp: ipv4_address: 172.25.0.11 elasticsearch: image: elasticsearch:2.2 networks: frontapp: ipv4_address: 172.25.0.12 postgres: image: postgres:9.5 environment: POSTGRES_USER: elephant POSTGRES_PASSWORD: smarty_pants POSTGRES_DB: elephant volumes: - /var/lib/postgresql/data networks: frontapp: ipv4_address: 172.25.0.10 networks: frontapp: driver: bridge ipam: driver: default config: - subnet: 172.25.0.0/16 gateway: 172.25.0.1
回答1:
There is a opensource application that solves this issue, it's called DNS Proxy Server
It's a DNS server that solves containers hostnames, if could not found a hostname with that hostname then solve it from internet as well
Start the DNS Server
$ docker run --hostname dns.mageddo --name dns-proxy-server -p 5380:5380 \ -v /var/run/docker.sock:/var/run/docker.sock \ -v /etc/resolv.conf:/etc/resolv.conf \ defreitas/dns-proxy-server
It will set as your default DNS automatically (and recover to the original when stops)
Start your container for test
docker-compose up
docker-compose.yml
version: '2' services: redis: container_name: redis image: redis:2.8 hostname: redis.dev.intranet network_mode: bridge # that way he can solve others containers names even inside, solve elasticsearch, for example elasticsearch: container_name: elasticsearch image: elasticsearch:2.2 hostname: elasticsearch.dev.intranet
Now solve your containers hostnames
from host
$ nslookup redis.dev.intranet Server: 172.17.0.2 Address: 172.17.0.2#53 Non-authoritative answer: Name: redis.dev.intranet Address: 172.21.0.3
from another container
$ docker exec -it redis ping elasticsearch.dev.intranet PING elasticsearch.dev.intranet (172.21.0.2): 56 data bytes
As well it solves internet hostnames
$ nslookup google.com Server: 172.17.0.2 Address: 172.17.0.2#53 Non-authoritative answer: Name: google.com Address: 216.58.202.78
回答2:
hostname of the docker container cannot be seen from outside. What you can do is to assign a name to container and access the container through the name. If you link 2 containers say container1 and container2 then docker takes care of writing the IP and the hostname of container2 in the container1. However in your case your application is running in the hostmachine.
OR
You know the IP of the container. So in your host machine's /etc/hosts you can add $IP $hostanameof container
回答3:
If you're only using you docker-compose setup locally you could map the ports from your containers to your host with
elasticsearch: image: elasticsearch:2.2 ports: - 9300:9300 - 9200:9200
Then use localhost:9300 (or 9200 depending on protocol) from your web-app to access Elasticsearch.
A more complex solution is to run your own dns that resolve container names. I think that this solution is a lot closer to what you're asking for. I have previsously used skydns when running kubernetes locally.
There are a few options out there. Have a look at https://github.com/gliderlabs/registrator and https://github.com/jderusse/docker-dns-gen. I didn't try it, but you could potentially map the dns port to your host in the same way as with the elastic ports in the previous example and then add localhost to your resolv.conf to be able to resolve your container names from your host.
回答4:
Aditya is correct. In your case the simplest is to hard code your hostname / IP maping in /etc/hosts
The problem with this approach, however, is that you do not control the private IP address your postgres machine will have. IP address will change every time you start a new container, and so you will need to update your /etc/hosts file.
If that's an issue, I would recommend that you read this blog post that explains how to enforce that a container get a specific IP address:
https://xand.es/2016/05/09/docker-with-known-ip/
回答5:
There are two solutions (except /etc/hosts) described here and here
I wrote my own solution in Python and implemented it as service to provide mapping from container hostname to its IP. Here it is: https://github.com/nicolai-budico/dockerhosts
It launches dnsmasq with parameter --hostsdir=/var/run/docker-hosts and updates file /var/run/docker-hosts/hosts each time a list of running containers was changed. Once file /var/run/docker-hosts/hosts is changed, dnsmasq automatically updates its mapping and container become available by hostname in a second.
$ docker run -d --hostname=myapp.local.com --rm -it ubuntu:17.10 9af0b6a89feee747151007214b4e24b8ec7c9b2858badff6d584110bed45b740 $ nslookup myapp.local.com Server: 127.0.0.53 Address: 127.0.0.53#53 Non-authoritative answer: Name: myapp.local.com Address: 172.17.0.2
There are install and uninstall scripts. Only you need is to allow your system to interact with this dnsmasq instance. I registered in in systemd-resolved:
$ cat /etc/systemd/resolved.conf [Resolve] DNS=127.0.0.54 #FallbackDNS= #Domains= #LLMNR=yes #MulticastDNS=yes #DNSSEC=no #Cache=yes #DNSStubListener=udp
