# Management Overview > Octelium documentation. Canonical page: . The *Core* API is the main API for *Cluster* management. The *Core* API includes resources such as [*Services*](https://octelium.com/docs/octelium/latest/management/core/service/overview.md), [*Namespaces*](https://octelium.com/docs/octelium/latest/management/core/namespace.md), [*Users*](https://octelium.com/docs/octelium/latest/management/core/user.md), [*Groups*](https://octelium.com/docs/octelium/latest/management/core/group.md), [*Policies*](https://octelium.com/docs/octelium/latest/management/core/policy.md), [*Devices*](https://octelium.com/docs/octelium/latest/management/core/device.md), [*ClusterConfig*](https://octelium.com/docs/octelium/latest/management/core/cluster-config.md) among other resource types. ## Applying Changes The *Cluster* is designed to be managed, using the `octeliumctl` CLI, in a centralized and declarative way that is very similar to Kubernetes via the `octeliumctl apply` command, through which you can apply all changes of your resources and (re)produce the state of your *Cluster* with a single command. You can define one or more resources in a single `yaml` file and then apply all changes as follows: ```bash octeliumctl apply ``` As your *Cluster*'s resources grow, you might want to define your resources in multiple `yaml` files and even organize them into further subdirectories. In a fairly complex system with at least tens or hundreds of resources, it's much better to organize your configuration into multiple files and subdirectories. Here is an example: ```text octelium ├── policies ├── http.yaml ├── devops.yaml ├── services ├── dbs ├── aws.yaml ├── azure.yaml ├── apis.yaml ├── ssh.yaml ├── users ├── contractors.yaml ├── employees ├── dev.yaml ├── ops.yaml ``` In such case, you similarly use the `octeliumctl apply` command as follows: ```bash octeliumctl apply ``` You can also apply changes to only a certain subdirectory or even a certain file. Here are some examples: ```bash # Only apply changes in /policies directory octeliumctl apply /policies # Only apply changes in /services/dbs directory octeliumctl apply /services/dbs # Only apply changes in /users/employees/ops.yaml file octeliumctl apply /users/employees/ops.yaml ``` By default, the `octeliumctl apply` command only applies changes to create or update exiting resources but does not delete nonexistent resources. If you want to completely synchronize the state described in your file/directory and prune all additional resources in the *Cluster* that no longer exist in the current configuration, you can add the `--prune` flag as follows: ```bash octeliumctl apply --prune ``` By default changes to all Resource types, except for *Secret* resources which are meant to be mainly managed in an imperative way (read more [here](https://octelium.com/docs/octelium/latest/management/core/secret.md)), are applied. You can also choose to apply changes for certain Resource types instead of applying changes to all types. For example, you can apply changes for *User* and *IdentityProvider* resources only as follows: ```bash octeliumctl apply --include User --include IdentityProvider ``` Now, only changes to `User` and `IdentityProvider` resources are applied. You can also exclude one or more types as follows: ```bash octeliumctl apply --exclude Service ``` You can also include *Secret* resources via the `--include-secret` flag as follows: ```bash octeliumctl apply --include-secret ``` ### Dry Run You can see the changes that would be applied to the *Cluster* without actually applying them via the `--dry-run` flag as follows: ```bash octeliumctl apply --dry-run ``` You can also see the resources that would be deleted by additionally using the `--prune` flag as follows: ```bash octeliumctl apply --dry-run --prune ``` > **Note:** > > The current resources are still fetched from the *Cluster* in order to compute the changes. However, the desired resources are not validated by the *Cluster* in the dry run mode. ### Validating Resources You can also strictly validate your desired state locally without connecting to the *Cluster* via the `octeliumctl validate` command. This command accepts the same files and directories as the `octeliumctl apply` command and reports all unknown fields, invalid enum values, invalid field types, unsupported kinds and duplicate resources at once. Here are some examples: ```bash # Validate a single file octeliumctl validate # Validate a root directory including all its yaml files and subdirectories octeliumctl validate # Validate multiple files and directories at once octeliumctl validate # Validate from stdin cat | octeliumctl validate - ``` The command exits with an error if any error is found which makes it useful, for example, in CI pipelines before actually applying the changes to the *Cluster*. Note that the resources are not validated by the *Cluster* itself in this mode. ## Listing Resources You can list the different *Cluster* resources via the `octeliumctl get` command. For example, you can list the *Cluster*'s *Services* as follows: ```bash octeliumctl get service # Or simply octeliumctl get svc # Or list by a certain Namespace octeliumctl get svc --namespace default # Or simply octeliumctl get svc -n production # Show a certain Service octeliumctl get svc nginx.production ``` You can also set the page and number of items per page for the list as follows: ```bash octeliumctl get svc --items-per-page 10 --page 2 ``` By default, the list is ordered by the creation date. You can, however, set order the list by name as follows: ```bash octeliumctl get svc --order-by-name ``` You can also reverse the order of the list as follows: ```bash octeliumctl get svc --order-reverse ``` By default, the output of a `octeliumctl get` command is formatted as a table. You can force the output to be formatted as YAML as follows: ```bash octeliumctl get svc -o yaml # OR octeliumctl get svc -o yml ``` You can also force the output to be formatted as JSON as follows: ```bash octeliumctl get svc -o json # You can also use jq octeliumctl get svc -o json | jq octeliumctl get sess -o json | jq -r .items[0].metadata.uid ``` ## Deleting Resources You can delete a certain resource via the `octeliumctl delete` command. Here are some examples: ```bash octeliumctl delete secret my-secret # OR octeliumctl del secret my-secret octeliumctl del svc nginx ```