There are two string operators. The first is the concatenation operator (‘.‘), which returns the concatenation of its right and left arguments. The second is the concatenating assignment operator (‘.=‘), which appends the argument on the right side to the argument on the left side. Show
Examples : Input : string1: Hello
string2 : World!
Output : HelloWorld!
Input : string1: geeksfor
string2: geeks
Output : geeksforgeeksCode #1: PHP
HelloWorld!0
HelloWorld!1 HelloWorld!2 =HelloWorld!4 HelloWorld!0
HelloWorld!6 HelloWorld!7 =$aJohn Carter!0 HelloWorld!2 HelloWorld!0
John Carter!3 John Carter!4 John Carter!5 HelloWorld!0 John Carter!7 Output HelloWorld! Time complexity : O(n) Code #2 : PHP
Hello World!0 =Hello World!2 HelloWorld!0
HelloWorld!1 Hello World!5 =Hello World!7 HelloWorld!0
HelloWorld!6 HelloWorld!7 =Hello World!0 John Carter!0 GeeksforGeeks4 John Carter!0 Hello World!5 HelloWorld!0
John Carter!3 John Carter!4 John Carter!5 HelloWorld!0 John Carter!7 Output John Carter! Time complexity : O(n) Code #3 : PHP
HelloWorld!0
HelloWorld!0
John Carter!4 // First String6HelloWorld!0 John Carter!7 Output Hello World! Time complexity : O(n) Code #4 : PHP
HelloWorld!0
HelloWorld!1 HelloWorld!2 =$a8HelloWorld!0
HelloWorld!7 ==3HelloWorld!0
John Carter!4 John Carter!5 HelloWorld!0 John Carter!7 Output GeeksforGeeks Time complexity : O(n) PHP is a server-side scripting language designed specifically for web development. You can learn PHP from the ground up by following this PHP Tutorial and PHP Examples. A Secret is an object that contains a small amount of sensitive data such as a password, a token, or a key. Such information might otherwise be put in a Pod specification or in a . Using a Secret means that you don't need to include confidential data in your application code. Because Secrets can be created independently of the Pods that use them, there is less risk of the Secret (and its data) being exposed during the workflow of creating, viewing, and editing Pods. Kubernetes, and applications that run in your cluster, can also take additional precautions with Secrets, such as avoiding writing secret data to nonvolatile storage. Secrets are similar to ConfigMaps but are specifically intended to hold confidential data. Caution: Kubernetes Secrets are, by default, stored unencrypted in the API server's underlying data store (etcd). Anyone with API access can retrieve or modify a Secret, and so can anyone with access to etcd. Additionally, anyone who is authorized to create a Pod in a namespace can use that access to read any Secret in that namespace; this includes indirect access such as the ability to create a Deployment. In order to safely use Secrets, take at least the following steps: For more guidelines to manage and improve the security of your Secrets, refer to Good practices for Kubernetes Secrets. See for more details. Uses for SecretsThere are three main ways for a Pod to use a Secret: The Kubernetes control plane also uses Secrets; for example, are a mechanism to help automate node registration. Alternatives to SecretsRather than using a Secret to protect confidential data, you can pick from alternatives. Here are some of your options:
You can also combine two or more of those options, including the option to use Secret objects themselves. For example: implement (or deploy) an operator that fetches short-lived session tokens from an external service, and then creates Secrets based on those short-lived session tokens. Pods running in your cluster can make use of the session tokens, and operator ensures they are valid. This separation means that you can run Pods that are unaware of the exact mechanisms for issuing and refreshing those session tokens. Working with SecretsCreating a SecretThere are several options to create a Secret: Constraints on Secret names and dataThe name of a Secret object must be a valid . You can specify the The keys of Size limitIndividual secrets are limited to 1MiB in size. This is to discourage creation of very large secrets that could exhaust the API server and kubelet memory. However, creation of many smaller secrets could also exhaust memory. You can use a resource quota to limit the number of Secrets (or other resources) in a namespace. Editing a SecretYou can edit an existing Secret unless it is . To edit a Secret, use one of the following methods: You can also edit the data in a Secret using the . However, this method creates a new Depending on how you created the Secret, as well as how the Secret is used in your Pods, updates to existing Using a SecretSecrets can be mounted as data volumes or exposed as environment variables to be used by a container in a Pod. Secrets can also be used by other parts of the system, without being directly exposed to the Pod. For example, Secrets can hold credentials that other parts of the system should use to interact with external systems on your behalf. Secret volume sources are validated to ensure that the specified object reference actually points to an object of type Secret. Therefore, a Secret needs to be created before any Pods that depend on it. If the Secret cannot be fetched (perhaps because it does not exist, or due to a temporary lack of connection to the API server) the kubelet periodically retries running that Pod. The kubelet also reports an Event for that Pod, including details of the problem fetching the Secret. Optional SecretsWhen you define a container environment variable based on a Secret, you can mark it as optional. The default is for the Secret to be required. None of a Pod's containers will start until all non-optional Secrets are available. If a Pod references a specific key in a Secret and that Secret does exist, but is missing the named key, the Pod fails during startup. Using Secrets as files from a PodIf you want to access data from a Secret in a Pod, one way to do that is to have Kubernetes make the value of that Secret be available as a file inside the filesystem of one or more of the Pod's containers. To configure that, you:
This is an example of a Pod that mounts a Secret named Each Secret you want to use needs to be referred to in If there are multiple containers in the Pod, then each container needs its own Note: Versions of Kubernetes before v1.22 automatically created credentials for accessing the Kubernetes API. This older mechanism was based on creating token Secrets that could then be mounted into running Pods. In more recent versions, including Kubernetes v1.26, API credentials are obtained directly by using the TokenRequest API, and are mounted into Pods using a . The tokens obtained using this method have bounded lifetimes, and are automatically invalidated when the Pod they are mounted into is deleted. You can still a service account token Secret; for example, if you need a token that never expires. However, using the TokenRequest subresource to obtain a token to access the API is recommended instead. You can use the command to obtain a token from the Projection of Secret keys to specific pathsYou can also control the paths within the volume where Secret keys are projected. You can use the What will happen:
If If you list keys explicitly, then all listed keys must exist in the corresponding Secret. Otherwise, the volume is not created. Secret files permissionsYou can set the POSIX file access permission bits for a single Secret key. If you don't specify any permissions, For example, you can specify a default mode like this: The secret is mounted on Note: If you're defining a Pod or a Pod template using JSON, beware that the JSON specification doesn't support octal notation. You can use the decimal value for the Consuming Secret values from volumesInside the container that mounts a secret volume, the secret keys appear as files. The secret values are base64 decoded and stored inside these files. This is the result of commands executed inside the container from the example above: The output is similar to: The output is similar to: The output is similar to: The program in a container is responsible for reading the secret data from these files, as needed. When a volume contains data from a Secret, and that Secret is updated, Kubernetes tracks this and updates the data in the volume, using an eventually-consistent approach. Note: A container using a Secret as a volume mount does not receive automated Secret updates. The kubelet keeps a cache of the current keys and values for the Secrets that are used in volumes for pods on that node. You can configure the way that the kubelet detects changes from the cached values. The Updates to Secrets can be either propagated by an API watch mechanism (the default), based on a cache with a defined time-to-live, or polled from the cluster API server on each kubelet synchronisation loop. As a result, the total delay from the moment when the Secret is updated to the moment when new keys are projected to the Pod can be as long as the kubelet sync period + cache propagation delay, where the cache propagation delay depends on the chosen cache type (following the same order listed in the previous paragraph, these are: watch propagation delay, the configured cache TTL, or zero for direct polling). Using Secrets as environment variablesTo use a Secret in an environment variable in a Pod:
This is an example of a Pod that uses a Secret via environment variables: Invalid environment variablesSecrets used to populate environment variables by the If you define a Pod with an invalid variable name, the failed Pod startup includes an event with the reason set to The output is similar to: Consuming Secret values from environment variablesInside a container that consumes a Secret using environment variables, the secret keys appear as normal environment variables. The values of those variables are the base64 decoded values of the secret data. This is the result of commands executed inside the container from the example above: The output is similar to: The output is similar to: Note: If a container already consumes a Secret in an environment variable, a Secret update will not be seen by the container unless it is restarted. There are third party solutions for triggering restarts when secrets change. Container image pull secretsIf you want to fetch container images from a private repository, you need a way for the kubelet on each node to authenticate to that repository. You can configure image pull secrets to make this possible. These secrets are configured at the Pod level. Using imagePullSecretsThe Manually specifying an imagePullSecretYou can learn how to specify Arranging for imagePullSecrets to be automatically attachedYou can manually create Using Secrets with static PodsYou cannot use ConfigMaps or Secrets with static Pods. Use casesUse case: As container environment variablesCreate a secret Create the Secret: Use Use case: Pod with SSH keysCreate a Secret containing some SSH keys: The output is similar to: You can also create a Caution: Think carefully before sending your own SSH keys: other users of the cluster may have access to the Secret. You could instead create an SSH private key representing a service identity that you want to be accessible to all the users with whom you share the Kubernetes cluster, and that you can revoke if the credentials are compromised. Now you can create a Pod which references the secret with the SSH key and consumes it in a volume: When the container's command runs, the pieces of the key will be available in: The container is then free to use the secret data to establish an SSH connection. Use case: Pods with prod / test credentialsThis example illustrates a Pod which consumes a secret containing production credentials and another Pod which consumes a secret with test environment credentials. You can create a The output is similar to: You can also create a secret for test environment credentials. The output is similar to: Note: Special characters such as In most shells, the easiest way to escape the password is to surround it with single quotes ( You do not need to escape special characters in passwords from files ( Now make the Pods: Add the pods to the same Apply all those objects on the API server by running: Both containers will have the following files present on their filesystems with the values for each container's environment: Note how the specs for the two Pods differ only in one field; this facilitates creating Pods with different capabilities from a common Pod template. You could further simplify the base Pod specification by using two service accounts:
The Pod specification is shortened to: Use case: dotfiles in a secret volumeYou can make your data "hidden" by defining a key that begins with a dot. This key represents a dotfile or "hidden" file. For example, when the following secret is mounted into a volume, The volume will contain a single file, called Note: Files beginning with dot characters are hidden from the output of Use case: Secret visible to one container in a PodConsider a program that needs to handle HTTP requests, do some complex business logic, and then sign some messages with an HMAC. Because it has complex application logic, there might be an unnoticed remote file reading exploit in the server, which could expose the private key to an attacker. This could be divided into two processes in two containers: a frontend container which handles user interaction and business logic, but which cannot see the private key; and a signer container that can see the private key, and responds to simple signing requests from the frontend (for example, over localhost networking). With this partitioned approach, an attacker now has to trick the application server into doing something rather arbitrary, which may be harder than getting it to read a file. Types of SecretWhen creating a Secret, you can specify its type using the Kubernetes provides several built-in types for some common usage scenarios. These types vary in terms of the validations performed and the constraints Kubernetes imposes on them. Built-in TypeUsageYou can define and use your own Secret type by assigning a non-empty string as the Kubernetes doesn't impose any constraints on the type name. However, if you are using one of the built-in types, you must meet all the requirements defined for that type. If you are defining a type of secret that's for public use, follow the convention and structure the secret type to have your domain name before the name, separated by a Opaque secretsThe output looks like: The Service account token SecretsA Since 1.22, this type of Secret is no longer used to mount credentials into Pods, and obtaining tokens via the TokenRequest API is recommended instead of using service account token Secret objects. Tokens obtained from the You should only create a service account token Secret object if you can't use the When using this Secret type, you need to ensure that the After the Secret is created, a Kubernetes controller fills in some other fields such as the The following example configuration declares a service account token Secret: After creating the Secret, wait for Kubernetes to populate the See the ServiceAccount documentation for more information on how service accounts work. You can also check the Docker config SecretsYou can use one of the following
The The Below is an example for a Note: If you do not want to perform the base64 encoding, you can choose to use the When you create these types of Secrets using a manifest, the API server checks whether the expected key exists in the When you do not have a Docker config file, or you want to use That command creates a Secret of type then the output is equivalent to this JSON document (which is also a valid Docker configuration file): Note: The The
Both values for the above two keys are base64 encoded strings. You can, of course, provide the clear text content using the The following manifest is an example of a basic authentication Secret: The basic authentication Secret type is provided only for convenience. You can create an The builtin type The following manifest is an example of a Secret used for SSH public/private key authentication: The SSH authentication Secret type is provided only for user's convenience. You could instead create an Caution: SSH private keys do not establish trusted communication between an SSH client and host server on their own. A secondary means of establishing trust is needed to mitigate "man in the middle" attacks, such as a TLS secretsKubernetes provides a builtin Secret type One common use for TLS secrets is to configure encryption in transit for an Ingress, but you can also use it with other resources or directly in your workload. When using this type of Secret, the The following YAML contains an example config for a TLS Secret: The TLS Secret type is provided for user's convenience. You can create an When creating a TLS Secret using The public/private key pair must exist before hand. The public key certificate for Note: A kubernetes.io/tls Secret stores the Base64-encoded DER data for keys and certificates. If you're familiar with PEM format for private keys and for certificates, the base64 data are the same as that format except that you omit the initial and the last lines that are used in PEM. For example, for a certificate, you do not include Bootstrap token SecretsA bootstrap token Secret can be created by explicitly specifying the Secret A bootstrap token Secret is usually created in the As a Kubernetes manifest, a bootstrap token Secret might look like the following: A bootstrap type Secret has the following keys specified under
The above YAML may look confusing because the values are all in base64 encoded strings. In fact, you can create an identical Secret using the following YAML: Immutable SecretsFEATURE STATE: Kubernetes lets you mark specific Secrets (and ConfigMaps) as immutable. Preventing changes to the data of an existing Secret has the following benefits:
Marking a Secret as immutableYou can create an immutable Secret by setting the You can also update any existing mutable Secret to make it immutable. Note: Once a Secret or ConfigMap is marked as immutable, it is not possible to revert this change nor to mutate the contents of the Information security for SecretsAlthough ConfigMap and Secret work similarly, Kubernetes applies some additional protection for Secret objects. Secrets often hold values that span a spectrum of importance, many of which can cause escalations within Kubernetes (e.g. service account tokens) and to external systems. Even if an individual app can reason about the power of the Secrets it expects to interact with, other apps within the same namespace can render those assumptions invalid. A Secret is only sent to a node if a Pod on that node requires it. For mounting secrets into Pods, the kubelet stores a copy of the data into a There may be several containers in a Pod. By default, containers you define only have access to the default ServiceAccount and its related Secret. You must explicitly define environment variables or map a volume into a container in order to provide access to any other Secret. There may be Secrets for several Pods on the same node. However, only the Secrets that a Pod requests are potentially visible within its containers. Therefore, one Pod does not have access to the Secrets of another Pod. Warning: Any containers that run with |
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