Docker-Docs/engine/swarm/configs.md

---
title: Store configuration data using Docker Configs
description: How to store configuration data separate from the runtime
keywords: swarm, configuration, configs
---

## About configs

Docker swarm service configs  allow you to store non-sensitive information,
such as configuration files, outside a service's image or running containers.
This allows you to keep your images as generic as possible, without the need to
bind-mount configuration files into the containers or use environment variables.

Configs operate in a similar way to [secrets](secrets.md), except that they are
not encrypted at rest and are mounted directly into the container's filesystem
without the use of RAM disks. Configs can be added or removed from a service at
any time, and services can share a config. You can even use configs in
conjunction with environment variables or labels, for maximum flexibility.
Config values can be generic strings or binary content (up to 500 kb in size).

> **Note**: Docker configs are only available to swarm services, not to
> standalone containers. To use this feature, consider adapting your container
> to run as a service with a scale of 1.

Configs are supported on both Linux and Windows services.

### Windows support

Docker includes support for configs on Windows containers, but there are differences
in the implementations, which are called out in the examples below. Keep the
following notable differences in mind:

- Config files with custom targets are not directly bind-mounted into Windows
  containers, since Windows does not support non-directory file bind-mounts.
  Instead, configs for a container are all mounted in
  `C:\ProgramData\Docker\internal\configs` (an implementation detail which
  should not be relied upon by applications) within the container. Symbolic
  links are used to point from there to the desired target of the config within
  the container. The default target is `C:\ProgramData\Docker\configs`.

- When creating a service which uses Windows containers, the options to specify
  UID, GID, and mode are not supported for configs. Configs are currently only
  accessible by administrators and users with `system` access within the
  container.

- On Windows, create or update a service using `--credential-spec` with the
  `config://<config-name>` format.  This passes the gMSA credentials file
  directly to nodes before a container starts. No gMSA credentials are written
  to disk on worker nodes. For more information, refer to
  [Deploy services to a swarm](services.md#gmsa-for-swarm).

## How Docker manages configs

When you add a config to the swarm, Docker sends the config to the swarm manager
over a mutual TLS connection. The config is stored in the Raft log, which is
encrypted. The entire Raft log is replicated across the other managers, ensuring
the same high availability guarantees for configs as for the rest of the swarm
management data.

When you grant a newly-created or running service access to a config, the config
is mounted as a file in the container. The location of the mount point within
the container defaults to `/<config-name>` in Linux containers. In Windows
containers, configs are all mounted into `C:\ProgramData\Docker\configs` and
symbolic links are created to the desired location, which defaults to
`C:\<config-name>`.

You can set the ownership (`uid` and `gid`) for the config, using either the
numerical ID or the name of the user or group. You can also specify the file
permissions (`mode`). These settings are ignored for Windows containers.

- If not set, the config is owned by the user running the container
  command (often `root`) and that user's default group (also often `root`).
- If not set, the config has world-readable permissions (mode `0444`), unless a
  `umask` is set within the container, in which case the mode is impacted by
  that `umask` value.

You can update a service to grant it access to additional configs or revoke its
access to a given config at any time.

A node only has access to configs if the node is a swarm manager or if it is
running service tasks which have been granted access to the config. When a
container task stops running, the configs shared to it are unmounted from the
in-memory filesystem for that container and flushed from the node's memory.

If a node loses connectivity to the swarm while it is running a task container
with access to a config, the task container still has access to its configs, but
cannot receive updates until the node reconnects to the swarm.

You can add or inspect an individual config at any time, or list all
configs. You cannot remove a config that a running service is
using. See [Rotate a config](configs.md#example-rotate-a-config) for a way to
remove a config without disrupting running services.

To update or roll back configs more easily, consider adding a version
number or date to the config name. This is made easier by the ability to control
the mount point of the config within a given container.

To update a stack, make changes to your Compose file, then re-run `docker
stack deploy -c <new-compose-file> <stack-name>`. If you use a new config in
that file, your services start using them. Keep in mind that configurations
are immutable, so you can't change the file for an existing service.
Instead, you create a new config to use a different file

You can run `docker stack rm` to stop the app and take down the stack. This
removes any config that was created by `docker stack deploy` with the same stack
name. This removes _all_ configs, including those not referenced by services and
those remaining after a `docker service update --config-rm`.

## Read more about `docker config` commands

Use these links to read about specific commands, or continue to the
[example about using configs with a service](#advanced-example-use-configs-with-a-nginx-service).

- [`docker config create`](../reference/commandline/config_create.md)
- [`docker config inspect`](../reference/commandline/config_inspect.md)
- [`docker config ls`](../reference/commandline/config_ls.md)
- [`docker config rm`](../reference/commandline/config_rm.md)

## Examples

This section includes graduated examples which illustrate how to use
Docker configs.

> **Note**: These examples use a single-Engine swarm and unscaled services for
> simplicity. The examples use Linux containers, but Windows containers also
> support configs.

### Defining and using configs in compose files

The `docker stack` command supports defining configs in a Compose file.
However, the `configs` key is not supported for `docker compose`. See
[the Compose file reference](../../compose/compose-file/index.md#configs) for details.

### Simple example: Get started with configs

This simple example shows how configs work in just a few commands. For a
real-world example, continue to
[Advanced example: Use configs with a Nginx service](#advanced-example-use-configs-with-a-nginx-service).

1.  Add a config to Docker. The `docker config create` command reads standard
    input because the last argument, which represents the file to read the
    config from, is set to `-`.

    ```bash
    $ echo "This is a config" | docker config create my-config -
    ```

2.  Create a `redis` service and grant it access to the config. By default,
    the container can access the config at `/my-config`, but
    you can customize the file name on the container using the `target` option.

    ```bash
    $ docker service create --name redis --config my-config redis:alpine
    ```

3.  Verify that the task is running without issues using `docker service ps`. If
    everything is working, the output looks similar to this:

    ```bash
    $ docker service ps redis

    ID            NAME     IMAGE         NODE              DESIRED STATE  CURRENT STATE          ERROR  PORTS
    bkna6bpn8r1a  redis.1  redis:alpine  ip-172-31-46-109  Running        Running 8 seconds ago
    ```

4.  Get the ID of the `redis` service task container using `docker ps`, so that
    you can use `docker container exec` to connect to the container and read the contents
    of the config data file, which defaults to being readable by all and has the
    same name as the name of the config. The first command below illustrates
    how to find the container ID, and the second and third commands use shell
    completion to do this automatically.

    ```bash
    $ docker ps --filter name=redis -q

    5cb1c2348a59

    $ docker container exec $(docker ps --filter name=redis -q) ls -l /my-config

    -r--r--r--    1 root     root            12 Jun  5 20:49 my-config

    $ docker container exec $(docker ps --filter name=redis -q) cat /my-config

    This is a config
    ```

5.  Try removing the config. The removal fails because the `redis` service is
    running and has access to the config.

    ```bash

    $ docker config ls

    ID                          NAME                CREATED             UPDATED
    fzwcfuqjkvo5foqu7ts7ls578   hello               31 minutes ago      31 minutes ago


    $ docker config rm my-config

    Error response from daemon: rpc error: code = 3 desc = config 'my-config' is
    in use by the following service: redis
    ```

6.  Remove access to the config from the running `redis` service by updating the
    service.

    ```bash
    $ docker service update --config-rm my-config redis
    ```

7.  Repeat steps 3 and 4 again, verifying that the service no longer has access
    to the config. The container ID is different, because the
    `service update` command redeploys the service.

    ```none
    $ docker container exec -it $(docker ps --filter name=redis -q) cat /my-config

    cat: can't open '/my-config': No such file or directory
    ```

8.  Stop and remove the service, and remove the config from Docker.

    ```bash
    $ docker service rm redis

    $ docker config rm my-config
    ```

### Simple example: Use configs in a Windows service

This is a very simple example which shows how to use configs with a Microsoft
IIS service running on Docker for Windows running Windows containers on
Microsoft Windows 10.  It is a naive example that stores the webpage in a config.

This example assumes that you have PowerShell installed.

1.  Save the following into a new file `index.html`.

    ```html
    <html lang="en">
      <head><title>Hello Docker</title></head>
      <body>
        <p>Hello Docker! You have deployed a HTML page.</p>
      </body>
    </html>
    ```
2.  If you have not already done so, initialize or join the swarm.

    ```powershell
    docker swarm init
    ```

3.  Save the `index.html` file as a swarm config named `homepage`.

    ```powershell
    docker config create homepage index.html
    ```

4.  Create an IIS service and grant it access to the `homepage` config.

    ```powershell
    docker service create
        --name my-iis
        --publish published=8000,target=8000
        --config src=homepage,target="\inetpub\wwwroot\index.html"
        microsoft/iis:nanoserver
    ```

5.  Access the IIS service at `http://localhost:8000/`. It should serve
    the HTML content from the first step.

6.  Remove the service and the config.

    ```powershell
    docker service rm my-iis

    docker config rm homepage
    ```

### Example: Use a templated config

To create a configuration in which the content will be generated using a
template engine, use the `--template-driver` parameter and specify the engine
name as its argument. The template will be rendered when container is created.

1.  Save the following into a new file `index.html.tmpl`.

    ```html
    <html lang="en">
      <head><title>Hello Docker</title></head>
      <body>
        <p>Hello {% raw %}{{ env "HELLO" }}{% endraw %}! I'm service {% raw %}{{ .Service.Name }}{% endraw %}.</p>
      </body>
    </html>
    ```

2.  Save the `index.html.tmpl` file as a swarm config named `homepage`. Provide
    parameter `--template-driver` and specify `golang` as template engine.

    ```bash
    $ docker config create --template-driver golang homepage index.html.tmpl
    ```

3.  Create a service that runs Nginx and has access to the environment variable
    HELLO and to the config.

    ```bash
    $ docker service create \
         --name hello-template \
         --env HELLO="Docker" \
         --config source=homepage,target=/usr/share/nginx/html/index.html \
         --publish published=3000,target=80 \
         nginx:alpine
    ```

4.  Verify that the service is operational: you can reach the Nginx server, and
    that the correct output is being served.

    ```bash
    $ curl http://0.0.0.0:3000

    <html lang="en">
      <head><title>Hello Docker</title></head>
      <body>
        <p>Hello Docker! I'm service hello-template.</p>
      </body>
    </html>
    ```

### Advanced example: Use configs with a Nginx service

This example is divided into two parts.
[The first part](#generate-the-site-certificate) is all about generating
the site certificate and does not directly involve Docker configs at all, but
it sets up [the second part](#configure-the-nginx-container), where you store
and use the site certificate as a series of secrets and the Nginx configuration
as a config. The example shows how to set options on the config, such as the
target location within the container and the file permissions (`mode`).

#### Generate the site certificate

Generate a root CA and TLS certificate and key for your site. For production
sites, you may want to use a service such as `Let’s Encrypt` to generate the
TLS certificate and key, but this example uses command-line tools. This step
is a little complicated, but is only a set-up step so that you have
something to store as a Docker secret. If you want to skip these sub-steps,
you can [use Let's Encrypt](https://letsencrypt.org/getting-started/) to
generate the site key and certificate, name the files `site.key` and
`site.crt`, and skip to
[Configure the Nginx container](#configure-the-nginx-container).

1.  Generate a root key.

    ```bash
    $ openssl genrsa -out "root-ca.key" 4096
    ```

2.  Generate a CSR using the root key.

    ```bash
    $ openssl req \
              -new -key "root-ca.key" \
              -out "root-ca.csr" -sha256 \
              -subj '/C=US/ST=CA/L=San Francisco/O=Docker/CN=Swarm Secret Example CA'
    ```

3.  Configure the root CA. Edit a new file called `root-ca.cnf` and paste
    the following contents into it. This constrains the root CA to only sign
    leaf certificates and not intermediate CAs.

    ```none
    [root_ca]
    basicConstraints = critical,CA:TRUE,pathlen:1
    keyUsage = critical, nonRepudiation, cRLSign, keyCertSign
    subjectKeyIdentifier=hash
    ```

4.  Sign the certificate.

    ```bash
    $ openssl x509 -req -days 3650 -in "root-ca.csr" \
                   -signkey "root-ca.key" -sha256 -out "root-ca.crt" \
                   -extfile "root-ca.cnf" -extensions \
                   root_ca
    ```

5.  Generate the site key.

    ```bash
    $ openssl genrsa -out "site.key" 4096
    ```

6.  Generate the site certificate and sign it with the site key.

    ```bash
    $ openssl req -new -key "site.key" -out "site.csr" -sha256 \
              -subj '/C=US/ST=CA/L=San Francisco/O=Docker/CN=localhost'
    ```

7.  Configure the site certificate. Edit a new file called `site.cnf` and
    paste the following contents into it. This constrains the site
    certificate so that it can only be used to authenticate a server and
    can't be used to sign certificates.

    ```none
    [server]
    authorityKeyIdentifier=keyid,issuer
    basicConstraints = critical,CA:FALSE
    extendedKeyUsage=serverAuth
    keyUsage = critical, digitalSignature, keyEncipherment
    subjectAltName = DNS:localhost, IP:127.0.0.1
    subjectKeyIdentifier=hash
    ```

8.  Sign the site certificate.

    ```bash
    $ openssl x509 -req -days 750 -in "site.csr" -sha256 \
        -CA "root-ca.crt" -CAkey "root-ca.key" -CAcreateserial \
        -out "site.crt" -extfile "site.cnf" -extensions server
    ```

9.  The `site.csr` and `site.cnf` files are not needed by the Nginx service, but
    you need them if you want to generate a new site certificate. Protect
    the `root-ca.key` file.

#### Configure the Nginx container

1.  Produce a very basic Nginx configuration that serves static files over HTTPS.
    The TLS certificate and key are stored as Docker secrets so that they
    can be rotated easily.

    In the current directory, create a new file called `site.conf` with the
    following contents:

    ```none
    server {
        listen                443 ssl;
        server_name           localhost;
        ssl_certificate       /run/secrets/site.crt;
        ssl_certificate_key   /run/secrets/site.key;

        location / {
            root   /usr/share/nginx/html;
            index  index.html index.htm;
        }
    }
    ```

2.  Create two secrets, representing the key and the certificate. You can store
    any file as a secret as long as it is smaller than 500 KB. This allows you
    to decouple the key and certificate from the services that use them.
    In these examples, the secret name and the file name are the same.

    ```bash
    $ docker secret create site.key site.key

    $ docker secret create site.crt site.crt
    ```

3.  Save the `site.conf` file in a Docker config. The first parameter is the
    name of the config, and the second parameter is the file to read it from.

    ```bash
    $ docker config create site.conf site.conf
    ```

    List the configs:

    ```bash
    $ docker config ls

    ID                          NAME                CREATED             UPDATED
    4ory233120ccg7biwvy11gl5z   site.conf           4 seconds ago       4 seconds ago
    ```


4.  Create a service that runs Nginx and has access to the two secrets and the
    config. Set the mode to `0440` so that the file is only readable by its
    owner and that owner's group, not the world.

    ```bash
    $ docker service create \
         --name nginx \
         --secret site.key \
         --secret site.crt \
         --config source=site.conf,target=/etc/nginx/conf.d/site.conf,mode=0440 \
         --publish published=3000,target=443 \
         nginx:latest \
         sh -c "exec nginx -g 'daemon off;'"
    ```

    Within the running containers, the following three files now exist:

    - `/run/secrets/site.key`
    - `/run/secrets/site.crt`
    - `/etc/nginx/conf.d/site.conf`

5.  Verify that the Nginx service is running.

    ```bash
    $ docker service ls

    ID            NAME   MODE        REPLICAS  IMAGE
    zeskcec62q24  nginx  replicated  1/1       nginx:latest

    $ docker service ps nginx

    NAME                  IMAGE         NODE  DESIRED STATE  CURRENT STATE          ERROR  PORTS
    nginx.1.9ls3yo9ugcls  nginx:latest  moby  Running        Running 3 minutes ago
    ```

6.  Verify that the service is operational: you can reach the Nginx
    server, and that the correct TLS certificate is being used.

    ```bash
    $ curl --cacert root-ca.crt https://0.0.0.0:3000

    <!DOCTYPE html>
    <html>
    <head>
    <title>Welcome to nginx!</title>
    <style>
        body {
            width: 35em;
            margin: 0 auto;
            font-family: Tahoma, Verdana, Arial, sans-serif;
        }
    </style>
    </head>
    <body>
    <h1>Welcome to nginx!</h1>
    <p>If you see this page, the nginx web server is successfully installed and
    working. Further configuration is required.</p>

    <p>For online documentation and support, refer to
    <a href="https://nginx.org">nginx.org</a>.<br/>
    Commercial support is available at
    <a href="https://www.nginx.com">www.nginx.com</a>.</p>

    <p><em>Thank you for using nginx.</em></p>
    </body>
    </html>
    ```

    ```bash
    $ openssl s_client -connect 0.0.0.0:3000 -CAfile root-ca.crt

    CONNECTED(00000003)
    depth=1 /C=US/ST=CA/L=San Francisco/O=Docker/CN=Swarm Secret Example CA
    verify return:1
    depth=0 /C=US/ST=CA/L=San Francisco/O=Docker/CN=localhost
    verify return:1
    ---
    Certificate chain
     0 s:/C=US/ST=CA/L=San Francisco/O=Docker/CN=localhost
       i:/C=US/ST=CA/L=San Francisco/O=Docker/CN=Swarm Secret Example CA
    ---
    Server certificate
    -----BEGIN CERTIFICATE-----
    …
    -----END CERTIFICATE-----
    subject=/C=US/ST=CA/L=San Francisco/O=Docker/CN=localhost
    issuer=/C=US/ST=CA/L=San Francisco/O=Docker/CN=Swarm Secret Example CA
    ---
    No client certificate CA names sent
    ---
    SSL handshake has read 1663 bytes and written 712 bytes
    ---
    New, TLSv1/SSLv3, Cipher is AES256-SHA
    Server public key is 4096 bit
    Secure Renegotiation IS supported
    Compression: NONE
    Expansion: NONE
    SSL-Session:
        Protocol  : TLSv1
        Cipher    : AES256-SHA
        Session-ID: A1A8BF35549C5715648A12FD7B7E3D861539316B03440187D9DA6C2E48822853
        Session-ID-ctx:
        Master-Key: F39D1B12274BA16D3A906F390A61438221E381952E9E1E05D3DD784F0135FB81353DA38C6D5C021CB926E844DFC49FC4
        Key-Arg   : None
        Start Time: 1481685096
        Timeout   : 300 (sec)
        Verify return code: 0 (ok)
    ```

7.  Unless you are going to continue to the next example, clean up after running
    this example by removing the `nginx` service and the stored secrets and
    config.

    ```bash
    $ docker service rm nginx

    $ docker secret rm site.crt site.key

    $ docker config rm site.conf
    ```

You have now configured a Nginx service with its configuration decoupled from
its image. You could run multiple sites with exactly the same image but
separate configurations, without the need to build a custom image at all.

### Example: Rotate a config

To rotate a config, you first save a new config with a different name than the
one that is currently in use. You then redeploy the service, removing the old
config and adding the new config at the same mount point within the container.
This example builds upon the previous one by rotating the `site.conf`
configuration file.

1.  Edit the `site.conf` file locally. Add `index.php` to the `index` line, and
    save the file.

    ```none
    server {
        listen                443 ssl;
        server_name           localhost;
        ssl_certificate       /run/secrets/site.crt;
        ssl_certificate_key   /run/secrets/site.key;

        location / {
            root   /usr/share/nginx/html;
            index  index.html index.htm index.php;
        }
    }
    ```

2.  Create a new Docker config using the new `site.conf`, called `site-v2.conf`.

    ```bah
    $ docker config create site-v2.conf site.conf
    ```

3.  Update the `nginx` service to use the new config instead of the old one.

    ```bash
    $ docker service update \
      --config-rm site.conf \
      --config-add source=site-v2.conf,target=/etc/nginx/conf.d/site.conf,mode=0440 \
      nginx
    ```

4.  Verify that the `nginx` service is fully re-deployed, using
    `docker service ps nginx`. When it is, you can remove the old `site.conf`
    config.

    ```bash
    $ docker config rm site.conf
    ```

5.  To clean up, you can remove the `nginx` service, as well as the secrets and
    configs.

    ```bash
    $ docker service rm nginx

    $ docker secret rm site.crt site.key

    $ docker config rm site-v2.conf
    ```

You have now updated your `nginx` service's configuration without the need to
rebuild its image.