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The State Store

kops has the notion of a 'state store'; a location where we store the configuration of your cluster. State is stored here not only when you first create a cluster, but also you can change the state and apply changes to a running cluster.

Eventually, kubernetes services will also pull from the state store, so that we don't need to marshal all our configuration through a channel like user-data. (This is currently done for secrets and SSL keys, for example, though we have to copy the data from the state store to a file where components like kubelet can read them).

The state store uses kops's VFS implementation, so can in theory be stored anywhere. Currently storage on S3 is supported, but support for GCS is coming soon, along with encrypted storage.

The state store is just files; you can copy the files down and put them into git (or your preferred version control system).

{statestore}/config

One of the most important files in the state store is the top-level config file. This file stores the main configuration for your cluster (instance types, zones, etc)\

When you run kops create cluster, we create a state store entry for you based on the command line options you specify. For example, when you run with --node-size=m4.large, we actually set a line in the configuration that looks like NodeMachineType: m4.large.

The configuration you specify on the command line is actually just a convenient short-cut to manually editing the configuration. Options you specify on the command line are merged into the existing configuration. If you want to configure advanced options, or prefer a text-based configuration, you may prefer to just edit the config file with kops edit cluster.

Because the configuration is merged, this is how you can just specify the changed arguments when reconfiguring your cluster - for example just kops create cluster after a dry-run.

Moving state between S3 buckets

The state store can easily be moved to a different s3 bucket. The steps for a single cluster are as follows:

  1. Recursively copy all files from ${OLD_KOPS_STATE_STORE}/${CLUSTER_NAME} to ${NEW_KOPS_STATE_STORE}/${CLUSTER_NAME} with aws s3 sync or a similar tool.
  2. Update the KOPS_STATE_STORE environment variable to use the new S3 bucket.
  3. Either run kops edit cluster ${CLUSTER_NAME} or edit the cluster manifest yaml file. Update .spec.configBase to reference the new s3 bucket.
  4. Run kops update cluster ${CLUSTER_NAME} --yes to apply the changes to the cluster. Newly launched nodes will now retrieve their dependent files from the new S3 bucket. The files in the old bucket are now safe to be deleted.

Repeat for each cluster needing to be moved.

State store configuration

There are a few ways to configure your state store. In priority order:

  • command line argument --state s3://yourstatestore
  • environment variable export KOPS_STATE_STORE=s3://yourstatestore
  • config file $HOME/.kops.yaml
  • config file $HOME/.kops/config

Configuration file example:

$HOME/.kops/config might look like this:

kops_state_store: s3://yourstatestore

Cross Account State-store (AWS)

There are situations in which the entity executing kops to create the cluster is not in the same account as the owner of the state store bucket. In this case, you must explicitly grant the permission: s3:getBucketLocation to the ARN that is running kops.

You can use the following policy to guide your implementation:

{
    "Id": "123",
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "123",
            "Action": [
                "s3:GetBucketLocation"
            ],
            "Effect": "Allow",
            "Resource": "arn:aws:s3:::state-store-bucket",
            "Principal": {
                "AWS": [
                    "arn:aws:iam::123456789:user/kopsuser"
                ]
            }
        }
    ]
}