The realtime glossary.
WebSockets, pub/sub and the concepts behind connected applications, in plain English. Clear definitions, practical examples and how each term relates to Pubb.
A
- App IDAuthentication & security
- An app ID identifies an application resource in a platform, allowing API requests and management operations to target the correct application.
- App keyAuthentication & security
- An app key is the client-facing identifier used to connect to a particular realtime application. In Pubb, it is designed to be included in browser or mobile configuration.
- App secretAuthentication & security
- An app secret is a confidential server credential that authorizes privileged operations for an application, such as publishing events and signing restricted subscriptions.
- AuthenticationAuthentication & security
- Authentication establishes who a requester is, usually by verifying a session, token or other credential before treating the requester as a particular user or service.
- AuthorizationAuthentication & security
- Authorization decides what an identified requester is allowed to do, such as reading a project's events or publishing an update to a shared room.
B
- BackpressureDelivery & reliability
- Backpressure is a system's response when data arrives faster than the next stage can process it, preventing work or buffered messages from growing without control.
- BandwidthPerformance & limits
- Bandwidth describes data-transfer capacity over time, commonly measured in bits or bytes per second. Event size and recipient count both affect the bandwidth a realtime application needs.
C
- ChannelMessaging basics
- A channel is a named destination that groups subscribers who should receive the same realtime events. Other messaging systems may call a similar destination a topic or room.
- Channel authorizationAuthentication & security
- Channel authorization is the server-side decision that a particular connection may subscribe to a restricted channel, followed by proof of that decision for the messaging service.
- Client SDKSDKs & infrastructure
- A client SDK is a library intended for the user-facing side of an application, commonly handling live connections, subscriptions and incoming event callbacks.
- Concurrent connectionsPerformance & limits
- Concurrent connections are the live connections open at the same time. They measure simultaneous connectivity rather than the number of registered or monthly active users.
- CORSAuthentication & security
- Cross-Origin Resource Sharing, or CORS, is a browser mechanism that uses HTTP response headers to control whether scripts may read responses from another origin.
D
- Delivery guaranteesDelivery & reliability
- Delivery guarantees describe whether a messaging system may lose, repeat or uniquely process messages within a specified scope and under stated failure conditions.
- Delivery receiptDelivery & reliability
- A delivery receipt is confirmation that a message reached a defined stage, such as a device or application handler. A read receipt is a separate signal about user interaction.
E
- Environment variablesSDKs & infrastructure
- Environment variables are named configuration values supplied to a running process, often used to keep deployment settings separate from application source code.
- EventMessaging basics
- An event is a named notification that something happened, usually accompanied by a payload containing the data needed to understand or respond to the change.
- Event payloadMessaging basics
- An event payload is the application data carried by a message, such as a record ID, changed fields or a small snapshot of current state.
- Exponential backoffDelivery & reliability
- Exponential backoff increases the delay between repeated attempts after failures, usually up to a maximum wait. Jitter adds randomness so clients do not all retry together.
F
- Fan-outMessaging basics
- Fan-out is the distribution of one published event to multiple subscribers. It turns a single producer action into many outgoing delivery attempts.
- Full-duplexConnections & protocols
- Full-duplex communication allows both ends of a connection to send data independently, without waiting for a request-response turn for each message.
H
- HeartbeatConnections & protocols
- A heartbeat is a periodic signal used to check whether a connection is still responsive. WebSocket ping and pong frames are one way to perform that check.
- HMAC-SHA256Authentication & security
- HMAC-SHA256 is a keyed message authentication construction that combines a shared secret with SHA-256 to produce a value used to verify message integrity and authenticity.
- Horizontal scalingSDKs & infrastructure
- Horizontal scaling adds more service instances to distribute work, rather than only increasing the resources assigned to one instance.
- HTTP 202 AcceptedDelivery & reliability
- HTTP 202 Accepted indicates that a request has been accepted for processing, while processing may still be incomplete when the response is sent.
- HTTP APIConnections & protocols
- An HTTP API exposes application operations through URLs, methods, headers and response codes, allowing software to exchange data using a request-response model.
I
- IdempotencyDelivery & reliability
- Idempotency means repeating an operation has the same intended effect as performing it once. In publishing APIs, an idempotency key can identify retries of one logical publication.
J
- JSONSDKs & infrastructure
- JSON is a text format for representing objects, arrays, strings, numbers, booleans and null, widely used to exchange structured data between applications.
L
- LatencyPerformance & limits
- Latency is the elapsed time between a chosen starting point and a resulting action, such as publishing an event and rendering it on a subscriber's screen.
- Long pollingConnections & protocols
- Long polling keeps an HTTP request open until new data is available or a timeout occurs, after which the client makes another request.
M
- Message historyDelivery & reliability
- Message history is a persistent record of past messages or events that an application can retrieve later, including after a client disconnects or a service restarts.
- Message orderingDelivery & reliability
- Message ordering describes the sequence in which events are delivered or processed and the scope within which that sequence is meaningful, such as one connection or one entity.
- Message quotaPerformance & limits
- A message quota limits the number of counted messaging operations within a defined accounting period. Its meaning depends on what the service counts and when that period resets.
- Message replayDelivery & reliability
- Message replay sends previously recorded events to a consumer so it can reconstruct state or catch up with changes it did not receive live.
- Multi-tenancySDKs & infrastructure
- Multi-tenancy lets multiple customer or organizational contexts share infrastructure while keeping their resources, access rules and data appropriately separated.
O
- Online presenceApplication patterns
- Online presence represents which users appear connected or active in a shared context, commonly based on live membership information and application activity signals.
- Optimistic updatesApplication patterns
- An optimistic update changes the interface before the server confirms an action, making the application feel responsive while it waits for the authoritative result.
P
- Payload sizePerformance & limits
- Payload size is the encoded byte length of an event's data. It differs from the number of characters displayed or the size of an in-memory object.
- PollingConnections & protocols
- Polling is a technique in which a client repeatedly requests current data on a schedule to discover whether anything has changed.
- Presence channelChannels & presence
- A presence channel combines authorized realtime messaging with information about the members currently subscribed, including membership changes.
- Presence memberChannels & presence
- A presence member is a user identity represented in a presence channel, optionally accompanied by application-defined information such as a display name or avatar.
- Private channelChannels & presence
- A private channel requires backend authorization before a client can subscribe, allowing an application to restrict realtime events to permitted users.
- Pub/subMessaging basics
- Pub/sub is a messaging pattern in which publishers send events to named channels and subscribers receive events from the channels they follow.
- Public channelChannels & presence
- A public channel allows subscription without a user-specific authorization check. Its events must be suitable for everyone who can connect to the application.
- PublisherMessaging basics
- A publisher is the part of an application that sends an event into a messaging system so that interested subscribers can react to it.
R
- Rate limitingPerformance & limits
- Rate limiting restricts how much work a caller or workspace can request within a period, helping keep demand within the service's supported capacity.
- Realtime messagingMessaging basics
- Realtime messaging delivers updates to connected applications as events happen, allowing interfaces to change without a page reload or a repeated request for new data.
- ReconnectionDelivery & reliability
- Reconnection creates a new live connection after the previous one closes or fails. A complete recovery flow also restores subscriptions and refreshes application state.
- Redis Pub/SubSDKs & infrastructure
- Redis Pub/Sub is a Redis messaging facility that distributes publications on named channels to clients currently subscribed to those channels.
S
- SDKSDKs & infrastructure
- A Software Development Kit, or SDK, packages APIs and supporting code for integrating a service in a particular language or runtime.
- Server SDKSDKs & infrastructure
- A server SDK is a library for trusted backend code that performs privileged service operations using credentials unavailable to distributed clients.
- Server-sent eventsConnections & protocols
- Server-sent events are a browser-supported mechanism for receiving a stream of text events from a server over HTTP, commonly through the EventSource API.
- Socket IDChannels & presence
- A socket ID identifies one live connection to a realtime service. It is a temporary connection identifier rather than a durable user or device identity.
- State synchronizationApplication patterns
- State synchronization keeps a client's view aligned with authoritative application data by combining initial reads, live updates and recovery after gaps or conflicts.
- SubscriberMessaging basics
- A subscriber is a client that registers interest in a channel and receives events routed to that channel while its subscription is active.
- SubscriptionChannels & presence
- A subscription is an active registration to receive events from a channel. Its lifecycle includes requesting access, confirming success and eventually leaving the channel.
T
- ThroughputPerformance & limits
- Throughput measures how much work a system handles over time, such as publications, delivery attempts or bytes processed per second.
- Time to liveDelivery & reliability
- Time to live, or TTL, is the period after which a stored value, lease or cached entry expires unless the system renews or replaces it.
- TLSAuthentication & security
- Transport Layer Security, or TLS, protects network traffic with encryption and integrity checks and supports authenticating the server through a certificate.
- Transactional outboxDelivery & reliability
- A transactional outbox records work to be dispatched in the same database transaction as the state that requires it, reducing the gap between committing data and scheduling an external action.
- Typing indicatorsApplication patterns
- Typing indicators are short-lived interface signals that another participant is composing a message. They describe transient activity rather than a durable chat record.
W
- WebhookSDKs & infrastructure
- A webhook is an HTTP request that one system sends to another system's endpoint when an event occurs, enabling server-to-server notifications.
- WebSocketConnections & protocols
- WebSocket is a protocol for maintaining a persistent connection over which a client and server can both send messages, without starting a new HTTP request for every update.
- WebSocket handshakeConnections & protocols
- A WebSocket handshake is the initial exchange that establishes a WebSocket connection and agrees to use the WebSocket protocol before application messages flow.
- WSSConnections & protocols
- WSS is the URL scheme for a WebSocket connection protected by TLS, which encrypts traffic in transit and authenticates the server through its certificate.
Put the terms into practice.
Connect a client, publish an event and choose who can listen.