<!--[metadata]>
+++
title = "Protect the Docker daemon socket"
description = "How to setup and run Docker with HTTPS"
keywords = ["docker, docs, article, example, https, daemon, tls, ca,  certificate"]
[menu.main]
parent = "smn_administrate"
weight = 5
+++
<![end-metadata]-->

# Protect the Docker daemon socket

By default, Docker runs via a non-networked Unix socket. It can also
optionally communicate using a HTTP socket.

If you need Docker to be reachable via the network in a safe manner, you can
enable TLS by specifying the `tlsverify` flag and pointing Docker's
`tlscacert` flag to a trusted CA certificate.

In the daemon mode, it will only allow connections from clients
authenticated by a certificate signed by that CA. In the client mode,
it will only connect to servers with a certificate signed by that CA.

> **Warning**:
> Using TLS and managing a CA is an advanced topic. Please familiarize yourself
> with OpenSSL, x509 and TLS before using it in production.

> **Warning**:
> These TLS commands will only generate a working set of certificates on Linux.
> Mac OS X comes with a version of OpenSSL that is incompatible with the
> certificates that Docker requires.

## Create a CA, server and client keys with OpenSSL

> **Note**: replace all instances of `$HOST` in the following example with the
> DNS name of your Docker daemon's host.

First generate CA private and public keys:

    $ openssl genrsa -aes256 -out ca-key.pem 2048
    Generating RSA private key, 2048 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]:
    State or Province Name (full name) [Some-State]:Queensland
    Locality Name (eg, city) []:Brisbane
    Organization Name (eg, company) [Internet Widgits Pty Ltd]:Docker Inc
    Organizational Unit Name (eg, section) []:Boot2Docker
    Common Name (e.g. server FQDN or YOUR name) []:$HOST
    Email Address []:Sven@home.org.au

Now that we have a CA, you can create a server key and certificate
signing request (CSR). Make sure that "Common Name" (i.e., server FQDN or YOUR
name) matches the hostname you will use to connect to Docker:

> **Note**: replace all instances of `$HOST` in the following example with the
> DNS name of your Docker daemon's host.

    $ openssl genrsa -out server-key.pem 2048
    Generating RSA private key, 2048 bit long modulus
    ......................................................+++
    ............................................+++
    e is 65537 (0x10001)
    $ openssl req -subj "/CN=$HOST" -new -key server-key.pem -out server.csr

Next, we're going to sign the public key with our CA:

Since TLS connections can be made via IP address as well as DNS name, they need
to be specified when creating the certificate. For example, to allow connections
using `10.10.10.20` and `127.0.0.1`:

    $ echo subjectAltName = IP:10.10.10.20,IP:127.0.0.1 > extfile.cnf

    $ openssl x509 -req -days 365 -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:

For client authentication, create a client key and certificate signing
request:

    $ openssl genrsa -out key.pem 2048
    Generating RSA private key, 2048 bit long modulus
    ...............................................+++
    ...............................................................+++
    e is 65537 (0x10001)
    $ openssl req -subj '/CN=client' -new -key key.pem -out client.csr

To make the key suitable for client authentication, create an extensions
config file:

    $ echo extendedKeyUsage = clientAuth > extfile.cnf

Now sign the public key:

    $ openssl x509 -req -days 365 -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:

After generating `cert.pem` and `server-cert.pem` you can safely remove the
two certificate signing requests:

    $ rm -v client.csr server.csr

With a default `umask` of 022, your secret keys will be *world-readable* and
writable for you and your group.

In order to protect your keys from accidental damage, you will want to remove their
write permissions. To make them only readable by you, change file modes as follows:

    $ chmod -v 0400 ca-key.pem key.pem server-key.pem

Certificates can be world-readable, but you might want to remove write access to
prevent accidental damage:

    $ chmod -v 0444 ca.pem server-cert.pem cert.pem

Now you can make the Docker daemon only accept connections from clients
providing a certificate trusted by our CA:

    $ docker -d --tlsverify --tlscacert=ca.pem --tlscert=server-cert.pem --tlskey=server-key.pem \
      -H=0.0.0.0:2376

To be able to connect to Docker and validate its certificate, you now
need to provide your client keys, certificates and trusted CA:

> **Note**: replace all instances of `$HOST` in the following example with the
> DNS name of your Docker daemon's host.

    $ docker --tlsverify --tlscacert=ca.pem --tlscert=cert.pem --tlskey=key.pem \
      -H=$HOST:2376 version

> **Note**:
> Docker over TLS should run on TCP port 2376.

> **Warning**:
> As shown in the example above, you don't have to run the `docker` client
> with `sudo` or the `docker` group when you use certificate authentication.
> That means anyone with the keys can give any instructions to your Docker
> daemon, giving them root access to the machine hosting the daemon. Guard
> these keys as you would a root password!

## Secure by default

If you want to secure your Docker client connections by default, you can move
the files to the `.docker` directory in your home directory -- and set the
`DOCKER_HOST` and `DOCKER_TLS_VERIFY` variables as well (instead of passing
`-H=tcp://$HOST:2376` and `--tlsverify` on every call).

    $ mkdir -pv ~/.docker
    $ cp -v {ca,cert,key}.pem ~/.docker
    $ export DOCKER_HOST=tcp://$HOST:2376 DOCKER_TLS_VERIFY=1

Docker will now connect securely by default:

    $ docker ps

## Other modes

If you don't want to have complete two-way authentication, you can run
Docker in various other modes by mixing the flags.

### Daemon modes

 - `tlsverify`, `tlscacert`, `tlscert`, `tlskey` set: Authenticate clients
 - `tls`, `tlscert`, `tlskey`: Do not authenticate clients

### Client modes

 - `tls`: Authenticate server based on public/default CA pool
 - `tlsverify`, `tlscacert`: Authenticate server based on given CA
 - `tls`, `tlscert`, `tlskey`: Authenticate with client certificate, do not
   authenticate server based on given CA
 - `tlsverify`, `tlscacert`, `tlscert`, `tlskey`: Authenticate with client
   certificate and authenticate server based on given CA

If found, the client will send its client certificate, so you just need
to drop your keys into `~/.docker/{ca,cert,key}.pem`. Alternatively,
if you want to store your keys in another location, you can specify that
location using the environment variable `DOCKER_CERT_PATH`.

    $ export DOCKER_CERT_PATH=~/.docker/zone1/
    $ docker --tlsverify ps

### Connecting to the secure Docker port using `curl`

To use `curl` to make test API requests, you need to use three extra command line
flags:

    $ curl https://$HOST:2376/images/json \
      --cert ~/.docker/cert.pem \
      --key ~/.docker/key.pem \
      --cacert ~/.docker/ca.pem
