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centos下修改docker连接docker_host默认方式为tls方式
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1.安装docker，请参考官网文档 centos下安装docker
2.安装完成应该可以使用docker的各种命令连接docker host。docker host运行在本机上，但与localhost不同。默认设置下，docker host（docker daemon）监听docker.sock。本机下应该有docker.sock文件，使得各种docker命令能够成功的在docker host上运行指令或者取回信息。下面将介绍如何修改默认的连接方式为tls方式。
3.openssl生成证书：
修改docker连接docker daemon连接方式为tls方式，需要前提条件是生成好的证书。证书可用openssl生成。建议新建一个文件夹用来存放将要生成的各种证书。CD到存放证书的目录
a.生成key和ca证书（生成key的时候输入的密码在后面生成证书的时候会多次用到,使用docker daemon host 的DNS名字代替下面的$HOST）：
$ openssl genrsa -aes256 -out ca-key.pem 4096
Generating RSA private key, 4096 bit long modulus
............................................................................................................................................................................................++
........++
e is 65537 (0x10001)
Enter pass phrase for ca-key.pem:
Verifying - Enter pass phrase for ca-key.pem:
$ openssl req -new -x509 -days 365 -key ca-key.pem -sha256 -out ca.pem
Enter pass phrase for ca-key.pem:
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Name (2 letter code) [AU]:SH
State or Province Name (full name) [Some-State]:ShangHai
Locality Name (eg, city) []:ShangHai
Organization Name (eg, company) [Internet Widgits Pty Ltd]:Company Name
Organizational Unit Name (eg, section) []:Sales
Common Name (e.g. server FQDN or YOUR name) []:$HOST
Email Address []:example@xxx.com
b.生成server-key和和csr文件（使用docker daemon host 的DNS名字代替下面的$HOST）
$ openssl genrsa -out server-key.pem
Generating RSA private key, bit long modulus
.....................................................................++
.................................................................................................++
e is (0x10001)
$ openssl req -subj "/CN=$HOST" -sha256 -new -key server-key.pem -out server.csr
c.使你的tls连接能通过ip地址方式，绑定本机IP（使用本机IP代替下面的$LOCALIP）
$ echo subjectAltName = IP:$LOCALIP,IP:127.0.0.1 > extfile.cnf$ openssl x509 -req -days -sha256 -in server.csr -CA ca.pem -CAkey ca-key.pem -CAcreateserial -out server-cert.pem -extfile extfile.cnf
Signature ok
subject=/CN=your.host.com
Getting CA Private Key
Enter pass phrase for ca-key.pem:
d.生成客户端访问需要的key和证书等文件
$ openssl genrsa -out key.pem
Generating RSA private key, bit long modulus
.........................................................++
................++
e is (0x10001)
$ openssl req -subj '/CN=client' -new -key key.pem -out client.csr
c.生成客户端证书配置文件
$ echo extendedKeyUsage = clientAuth > extfile.cnf
d.注册key
$ openssl x509 -req -days -sha256 -in client.csr -CA ca.pem -CAkey ca-key.pem -CAcreateserial -out cert.pem -extfile extfile.cnf
Signature ok
subject=/CN=client
Getting CA Private Key
Enter pass phrase for ca-key.pem:
4.将生成的证书添加的docker的配置文件中，centos下docker的配置文件是/etc/sysconfig/docker,编辑配置文件
vi /etc/sysconfig/docker
5.修改配置文件OPTIONS配置（下面的证书地址换成你生成的对应证书的位置）
OPTIONS='--selinux-enabled --tlsverify --tlscacert=/etc/docker/ca.pem --tlscert=/var/docker/server-cert.pem --tlskey=/var/docker/server-key.pem -H tcp://0.0.0.0:2376'
6.保存退出，重启docker服务，输入docker images查看镜像
docker images
Get http://10.32.173.215:2376/v1.20/images/json: malformed HTTP response "\x15\x03\x01\x00\x02\x02".
* Are you trying to connect to a TLS-enabled daemon without TLS?
* Is your docker daemon up and running?
显示不能连接到docker daemon host。虽然docker daemon已经配置好并且重新启动了，但是相当于服务端更改了配置。所以客户端连接到docker daemon host的配置也需要修改。
7.修改docker连接配置
a.在root目录下创建目录.docker
mkdir ~/.docker
b.将客户端证书文件copy至.docker目录
cp -cv {ca,cert,key}.pem ~/.docker/
c.添加环境变量DOCKER_HOST和DOCKER_TLS_VERIFY
vi /etc/profile
d.在打开的文件中最后加上新的环境变量($YOURIP替换成docker daemon host的IP即本机IP)
export DOCKER_HOST=tcp://$YOURIP:2376
export DOCKER_TLS_VERIFY=
8.配置完成，输入docker images可连接docker daemon host查看镜像。至此，docker daemon host连接方式已经修改为tls方式。调用远程API的时候需要使用的证书就是~/.docker文件夹中的证书。
