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Configuring File Synchronization

The code synchronization feature of DevSpace allows you to use hot reloading during development. Especially when using programming languages and frameworks that support hot reloading with tools like nodemon, re-building and re-deploying containers is very annoying and time consuming. Therefore, DevSpace uses a smart syncing mechanism that is able to sync local file changes to remote containers directly without the need of rebuilding or restarting the container.

When starting the development mode, DevSpace starts the file sync as configured in the dev.sync section of the devspace.yaml.

images:
  backend:
    image: john/devbackend
  backend-debugger:
    image: john/debugger
deployments:
- name: app-backend
  component:
    containers:
    - image: john/devbackend
    - image: john/debugger
dev:
  sync:
  - imageName: backend
    localSubPath: ./
    containerPath: /app
    excludePaths:
    - node_modules/
    - logs/

Every sync configuration consists of two essential parts:

Additionally, there are several advanced options:

Container Selection

The following config options are needed to determine the container which the file synchronization should be established.

You can set either labelSelector (optionally in combination with containerName) or imageName. Both options can be combined with the optional namespace option if needed.

dev.sync[*].imageName

The imageName option expects a string with the name of an image from the images section of the devspace.yaml. Using imageName tells DevSpace to select the container based on the referenced image that was last built using DevSpace.

Using imageName is not possible if multiple deployments use the same image that belongs to this imageName referencing the images section of the devspace.yaml.

You cannot use the imageName option in combination with labelSelector.

Example: Select Container by Image

images:
  backend:
    image: john/devbackend
  backend-debugger:
    image: john/debugger
deployments:
- name: app-backend
  component:
    containers:
    - name: container-0
      image: john/devbackend
    - name: container-1
      image: john/debugger
dev:
  sync:
  - imageName: backend
    excludePaths:
    - node_modules/
    - logs/
  - imageName: backend-debugger
    localSubPath: ./debug-logs
    containerPath: /logs

Explanation:

  • The above example defines two images that can be used as imageName: backend and backend-debugger
  • The deployment starts two containers and each of them uses an image from the images section.
  • The imageName option of the first sync configuration in the dev.sync section references backend. That means DevSpace would select the first container for file synchronzation, as this container uses the image: john/devbackend which belongs to the backend image as defined in the images section.
  • The first sync configuration does not define localSubPath, so it defaults to the project's root directory (location of devspace.yaml).
  • The first sync configuration does not define containerPath, so it defaults to the container's working directory (i.e. WORKDIR).
  • The imageName option of the second sync configuration in the dev.sync section references backend-debugger. That means DevSpace would select the second container for file synchronization, as this container uses the image: john/debugger which belongs to the backend-debugger image as defined in the images section.

In consequence, the following sync processes would be started when using the above config example assuming the local project root directoy /my/project/:

  1. localhost:/my/project/ forwards to container-0:$WORKDIR *
  2. localhost:/my/project/debug-logs/ forwards to container-1:/logs

* Changes on either side (local and container filesystem) that occur within the sub-folders node_modules/ and logs/ would be ingored.

dev.sync[*].labelSelector

The labelSelector option expects a key-value map of strings with Kubernetes labels.

You cannot use the labelSelector option in combination with imageName.

Example: Select Container by Label

images:
  backend:
    image: john/devbackend
  backend-debugger:
    image: john/debugger
deployments:
- name: app-backend
  component:
    containers:
    - name: container-0
      image: john/devbackend
    - name: container-1
      image: john/debugger
dev:
  sync:
  - labelSelector:
      app.kubernetes.io/name: devspace-app
      app.kubernetes.io/component: app-backend
      custom-label: custom-label-value
    containerName: container-0
    localSubPath: ./src
    containerPath: /app/src

Explanation:

  • The labelSelector would select the pod created for the component deployment app-backend.
  • Because the selected pod has two containers, we also need to specify the containerName option which defines the container that should be used for the file synchronization.

dev.sync[*].containerName

The containerName option expects a string with a container name. This option is used to decide which container should be selected when using labelSelector option because labelSelector selects a pod and a pod can have multiple containers.

The containerName option is not required when the pod you are selecting using labelSelector has only one container.

Example

See "Example: Select Container by Label"

dev.sync[*].namespace

The namespace option expects a string with a Kubernetes namespace used to select the container from.

It is generally not needed to specify the namespace option because by default, DevSpace uses the default namespace of your current kube-context which is usually the one that has been used to deploy your containers to.

Sync Path Mapping

dev.sync[*].localSubPath

The localSubPath option expects a string with a path that is relative to the location of devspace.yaml.

Default Value For localSubPath

localSubPath: ./ # Project root directory (folder containing devspace.yaml)

Example

See "Example: Select Container by Image"

dev.sync[*].containerPath

The containerPath option expects a string with an absolute path on the container filesystem.

Default Value For containerPath

containerPath: $WORKDIR # working directory, set as WORKDIR in the Dockerfile

Example

See "Example: Select Container by Image"

Exclude Paths

The config options for excluding paths use the same syntax as .gitignore.

An exclude path that matches a folder recursively excludes all files and sub-folders within this folder.

dev.sync[*].excludePaths

The excludePaths option expects an array of strings with paths that should not be synchronized between the local filesystem and the remote container filesystem.

Default Value For excludePaths

excludePaths: [] # Do not exclude anything from file synchronization

Example: Exclude Paths from Synchronization

images:
  backend:
    image: john/devbackend
  backend-debugger:
    image: john/debugger
deployments:
- name: app-backend
  component:
    containers:
    - image: john/devbackend
    - image: john/debugger
dev:
  sync:
  - imageName: backend
    excludePaths:
    - logs/
    - more/logs/
    uploadExcludePaths:
    - node_modules/
    downloadExcludePaths:
    - tmp/

Explanation:

  • Files in logs/ and in mode/logs/ would not be synchronized at all.
  • Files in node_modules/ would only be synchroniyed from the container to the local filesystem but not the other way around.
  • Files in tmp/ would only be synchroniyed from the local to the container filesystem but not the other way around.

dev.sync[*].downloadExcludePaths

The downloadExcludePaths option expects an array of strings with paths that should not be synchronized from the remote container filesystem to the local filesystem.

Default Value For downloadExcludePaths

downloadExcludePaths: [] # Do not exclude anything from file synchronization

Example

See "Example: Exclude Paths from Synchronization"

dev.sync[*].uploadExcludePaths

The uploadExcludePaths option expects an array of strings with paths that should not be synchronized from the local filesystem to the remote container filesystem.

This option is often useful if you want to download a dependency folder (e.g. node_modules/) for code completion but you never want to upload anything from there because of compiled binaries that are not portable between local filesystem and container filesystem (e.g. when your local system is Windows but your containers run Linux).

Default Value For uploadExcludePaths

uploadExcludePaths: [] # Do not exclude anything from file synchronization

Example

See "Example: Exclude Paths from Synchronization"

Initial Sync

dev.sync[*].waitInitialSync

The waitInitialSync option expects a boolean which defines if DevSpace should wait until the initial sync process has terminated before opening the container terminal or the multi-container log streaming.

Default Value For waitInitialSync

waitInitialSync: false # Start container terminal or log streaming before initil sync is completed

Example: Exclude Paths from Synchronization

images:
  backend:
    image: john/devbackend
  backend-debugger:
    image: john/debugger
deployments:
- name: app-backend
  component:
    containers:
    - image: john/devbackend
    - image: john/debugger
dev:
  sync:
  - imageName: backend
    waitInitialSync: true

Explanation:
With the configuration devspace dev would do the following:

  • DevSpace would start port-forwarding and file synchronzation.
  • Initial sync would be started automatically.
  • After the initial sync process is finished, DevSpace starts the multi-container log streaming.

Network Bandwidth Limits

Sometimes it is useful to throttle the file synchronization, especially when large files or a large number of files are expected to change during development. The following config options provide these capabilities:

dev.sync[*].bandwidthLimits.download

The bandwidthLimits.download option expects an integer representing the max file download speed in KB/s, e.g. download: 100 would limit the file sync to a download speed of 100 KB/s.

By default, the file synchronization algorithm uses the maximum bandwidth possible to make the sync process as fast as possible.

Example: Limiting Network Bandwidth

images:
  backend:
    image: john/devbackend
  backend-debugger:
    image: john/debugger
deployments:
- name: app-backend
  component:
    containers:
    - image: john/devbackend
    - image: john/debugger
dev:
  sync:
  - imageName: backend
    bandwidthLimits:
      download: 200
      upload: 100

Explanation:

  • Downloading files from the container to the local filesystem would be limited to a transfer speed of 200 KB/s.
  • Upload files from the local filesystem to the container would be limited to a transfer speed of 100 KB/s.

dev.sync[*].bandwidthLimits.upload

The bandwidthLimits.upload option expects an integer representing the max file upload speed in KB/s, e.g. upload: 100 would limit the file sync to a upload speed of 100 KB/s.

By default, the file synchronization algorithm uses the maximum bandwidth possible to make the sync process as fast as possible.

Example

See "Example: Limiting Network Bandwidth"


Useful Commands

devspace add sync --local=[PATH] --container=[PATH]

Use the convenience command devspace add sync --local=[PATH] --container=[PATH] to tell DevSpace to add another sync path mapping to the dev.sync section of the devspace.yaml.

devspace add sync --local=src/ --container=/app/src

The example above would tell DevSpace to add a sync configuration for synchronizing the local path ./src/ with the container path /app/src.

devspace status sync

To get information about current synchronization activities, simply run:

devspace status sync

Additionally, you can ciew the sync log within .devspace/logs/sync.log to get more detailed information.

devspace sync

If you want to start file synchronzation on-demand without having to configure it in devspace.yaml and without starting port-forwarding or log streaming etc, you can use the devspace sync command as shown in the examples below:

# Select pod with a picker
devspace sync --local-path=subfolder --container-path=/app

# Select pod and container by name and use current working directory as local-path
devspace sync --pod=my-pod --container=my-container --container-path=/app

FAQ

How does the sync work?

DevSpace establishes a bi-directional code synchronization between the specified local folders and the remote container folders. It automatically recognizes any changes within the specified folders during the session and will update the corresponding files locally and remotely in the background. It uses a small helper binary that is injected into the target container to accomplish this.

The algorithm roughly works like this:

  1. Inject a small helper binary via kubectl cp into the target container
  2. Download all files that are not found locally
  3. Upload all files that are not found remotely
  4. Watches locally and remotely for changes and uploads or downloads them

Are there any requirements for the sync to work?

 The tar command has to be present in the container otherwise kubectl cp does not work and the helper binary cannot be injected into the container.

Other than that, no server-side component or special container privileges for code synchronization are required, as the sync algorithm runs completely client-only within DevSpace. The synchronization mechanism works with any container filesystem and no special binaries have to be installed into the containers. File watchers running within the containers like nodemon will also recognize changes made by the synchronization mechanism.

How does the initial sync right after devspace dev work?

 If synchronization is started, the sync initially compares the remote folder and the local folder and merges the contents with the following rules:

  • If a file or folder exists remote, but not locally, then download file / folder
  • If a file or folder exists locally, but not remote, then upload file / folder
  • If a file is newer locally than remote then upload the file (The opposite case is not true, older local files are not overriden by newer remote files)

What is the performance impact on using the file sync?

 The sync mechanism is normally very reliable and fast. Syncing several thousand files is usually not a problem. Changes are packed together and compressed during synchronization, which improves performance especially for transferring text files. Transferring large compressed binary files is possible, however can affect performance negatively. Remote changes can sometimes have a delay of 1-2 seconds till they are downloaded, depending on how big the synchronized folder is. It should be generally avoided to sync the complete container filesystem.

Last updated on 2019-9-16
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