docker

+++ title = "docker" description = "docker use docker for service discovery." weight = 10 tags = [ "plugin" , "docker" , "discovery" ] categories = [ "plugin", "external" ] date = "2021-05-03T10:26:00+03:00" repo = "github.com/rb-coredns/coredns-docker-discovery" home = "https://github.com/rb-coredns/coredns-docker-discovery/blob/master/README.md" +++

coredns-docker-discovery

Docker discovery plugin for coredns

Based on kevinjqiu/coredns-dockerdiscovery but with some big changes:

• use official golang docker client github.com/docker/docker instead of github.com/fsouza/go-dockerclient
• use default Docker endpoint from official driver
• add metrics!
• change log to coredns logger - clog
• updated dependencies (caddy to coredns)
• update tests to run on Windows and Linux without any problems
• some code cleanup
• change docker event listening logic
• configurable TTL for A answer

ToDo

• Support docker tls config in params block

Name

docker - add/remove DNS records for docker containers based on docker container and network events.

Syntax

docker [DOCKER_ENDPOINT] {
    domain DOMAIN_NAME
    hostname_domain HOSTNAME_DOMAIN_NAME
    network_aliases DOCKER_NETWORK
    label LABEL
    ttl TTL
}

• DOCKER_ENDPOINT: the path to the docker socket. If unspecified, defaults to unix:///var/run/docker.sock. It can also be TCP socket, such as tcp://127.0.0.1:999.
• DOMAIN_NAME: the name of the domain for container name, e.g. when DOMAIN_NAME is docker.loc, your container with my-nginx (as subdomain) name will be assigned the domain name: my-nginx.docker.loc
• HOSTNAME_DOMAIN_NAME: the name of the domain for hostname. Work same as DOMAIN_NAME for hostname.
• DOCKER_NETWORK: the name of the docker network. Resolve directly by network aliases (like internal docker dns resolve host by aliases whole network)
• LABEL: container label of resolving host (by default enable and equals coredns.dockerdiscovery.host)
• TTL: ttl for domain (by default 3600)

How To Build

GO111MODULE=on go get -u github.com/coredns/coredns
GO111MODULE=on go get github.com/rb-coredns/coredns-docker-discovery
cd ~/go/src/github.com/coredns/coredns
echo "docker:github.com/rb-coredns/coredns-docker-discovery" >> plugin.cfg
cat plugin.cfg | uniq > plugin.cfg
make all
~/go/src/github.com/coredns/coredns/coredns --version

Alternatively, you can use the following manual steps:

1. Checkout coredns: go get github.com/coredns/coredns.
2. cd $GOPATH/src/github.com/coredns/coredns
3. echo "docker:github.com/rb-coredns/coredns-dockerdiscovery" >> plugin.cfg
4. go generate
5. make

Alternatively, run insider docker container

docker build -t coredns-dockerdiscovery .
docker run --rm -v ${PWD}/Corefile:/etc/Corefile -v /var/run/docker.sock:/var/run/docker.sock -p 15353:15353/udp coredns-dockerdiscovery -conf /etc/Corefile

Run tests

go test -v

Example

Corefile:

.:15353 {
    docker unix:///var/run/docker.sock {
        domain docker.loc
        hostname_domain docker-host.loc
    }
    log
    debug
}

Start CoreDNS:

$ ./coredns
[DEBUG] plugin/docker: start
.:15353
CoreDNS-1.8.3
windows/amd64, go1.16.3, 

Start a docker container:

$ docker run -d --name my-alpine --hostname alpine alpine sleep 1000
78c2a06ef2a9b63df857b7985468f7310bba0d9ea4d0d2629343aff4fd171861

Use CoreDNS as your resolver to resolve the my-alpine.docker.loc or alpine.docker-host.loc:

$ dig @localhost -p 15353 my-alpine.docker.loc

; <<>> DiG 9.10.3-P4-Ubuntu <<>> @localhost -p 15353 my-alpine.docker.loc
; (1 server found)
;; global options: +cmd
;; Got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 61786
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1

;; OPT PSEUDOSECTION:
; EDNS: version: 0, flags:; udp: 4096
;; QUESTION SECTION:
;my-alpine.docker.loc.            IN      A

;; ANSWER SECTION:
my-alpine.docker.loc.     3600    IN      A       172.17.0.2

;; Query time: 0 msec
;; SERVER: 127.0.0.1#15353(127.0.0.1)
;; WHEN: Thu Apr 26 22:39:55 EDT 2018
;; MSG SIZE  rcvd: 63

Stop the docker container will remove the corresponded DNS entries:

$ docker stop my-alpine
78c2a

$ dig @localhost -p 15353 my-alpine.docker.loc

;; QUESTION SECTION:
;my-alpine.docker.loc.            IN      A

Container will be resolved by label as nginx.loc

docker run --label=coredns.dockerdiscovery.host=nginx.loc nginx

Local Development

See receipt how install for local development