StartLiveTailCommand

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Starts a Live Tail streaming session for one or more log groups. A Live Tail session returns a stream of log events that have been recently ingested in the log groups. For more information, see Use Live Tail to view logs in near real time .

The response to this operation is a response stream, over which the server sends live log events and the client receives them.

The following objects are sent over the stream:

  • A single LiveTailSessionStart  object is sent at the start of the session.

  • Every second, a LiveTailSessionUpdate  object is sent. Each of these objects contains an array of the actual log events.

    If no new log events were ingested in the past second, the LiveTailSessionUpdate object will contain an empty array.

    The array of log events contained in a LiveTailSessionUpdate can include as many as 500 log events. If the number of log events matching the request exceeds 500 per second, the log events are sampled down to 500 log events to be included in each LiveTailSessionUpdate object.

    If your client consumes the log events slower than the server produces them, CloudWatch Logs buffers up to 10 LiveTailSessionUpdate events or 5000 log events, after which it starts dropping the oldest events.

  • A SessionStreamingException  object is returned if an unknown error occurs on the server side.

  • A SessionTimeoutException  object is returned when the session times out, after it has been kept open for three hours.

The StartLiveTail API routes requests to streaming-logs.Region.amazonaws.com using SDK host prefix injection. VPC endpoint support is not available for this API.

You can end a session before it times out by closing the session stream or by closing the client that is receiving the stream. The session also ends if the established connection between the client and the server breaks.

For examples of using an SDK to start a Live Tail session, see Start a Live Tail session using an Amazon Web Services SDK .

Example Syntax

Use a bare-bones client and the command you need to make an API call.

import { CloudWatchLogsClient, StartLiveTailCommand } from "@aws-sdk/client-cloudwatch-logs"; // ES Modules import
// const { CloudWatchLogsClient, StartLiveTailCommand } = require("@aws-sdk/client-cloudwatch-logs"); // CommonJS import
const client = new CloudWatchLogsClient(config);
const input = { // StartLiveTailRequest
  logGroupIdentifiers: [ // StartLiveTailLogGroupIdentifiers // required
    "STRING_VALUE",
  ],
  logStreamNames: [ // InputLogStreamNames
    "STRING_VALUE",
  ],
  logStreamNamePrefixes: [
    "STRING_VALUE",
  ],
  logEventFilterPattern: "STRING_VALUE",
};
const command = new StartLiveTailCommand(input);
const response = await client.send(command);
// { // StartLiveTailResponse
//   responseStream: { // StartLiveTailResponseStream Union: only one key present
//     sessionStart: { // LiveTailSessionStart
//       requestId: "STRING_VALUE",
//       sessionId: "STRING_VALUE",
//       logGroupIdentifiers: [ // StartLiveTailLogGroupIdentifiers
//         "STRING_VALUE",
//       ],
//       logStreamNames: [ // InputLogStreamNames
//         "STRING_VALUE",
//       ],
//       logStreamNamePrefixes: [
//         "STRING_VALUE",
//       ],
//       logEventFilterPattern: "STRING_VALUE",
//     },
//     sessionUpdate: { // LiveTailSessionUpdate
//       sessionMetadata: { // LiveTailSessionMetadata
//         sampled: true || false,
//       },
//       sessionResults: [ // LiveTailSessionResults
//         { // LiveTailSessionLogEvent
//           logStreamName: "STRING_VALUE",
//           logGroupIdentifier: "STRING_VALUE",
//           message: "STRING_VALUE",
//           timestamp: Number("long"),
//           ingestionTime: Number("long"),
//         },
//       ],
//     },
//     SessionTimeoutException: { // SessionTimeoutException
//       message: "STRING_VALUE",
//     },
//     SessionStreamingException: { // SessionStreamingException
//       message: "STRING_VALUE",
//     },
//   },
// };

StartLiveTailCommand Input

See StartLiveTailCommandInput for more details

Parameter
Type
Description
logGroupIdentifiers
Required
string[] | undefined

An array where each item in the array is a log group to include in the Live Tail session.

Specify each log group by its ARN.

If you specify an ARN, the ARN can't end with an asterisk (*).

You can include up to 10 log groups.

logEventFilterPattern
string | undefined

An optional pattern to use to filter the results to include only log events that match the pattern. For example, a filter pattern of error 404 causes only log events that include both error and 404 to be included in the Live Tail stream.

Regular expression filter patterns are supported.

For more information about filter pattern syntax, see Filter and Pattern Syntax .

logStreamNamePrefixes
string[] | undefined

If you specify this parameter, then only log events in the log streams that have names that start with the prefixes that you specify here are included in the Live Tail session.

If you specify this field, you can't also specify the logStreamNames field.

You can specify this parameter only if you specify only one log group in logGroupIdentifiers.

logStreamNames
string[] | undefined

If you specify this parameter, then only log events in the log streams that you specify here are included in the Live Tail session.

If you specify this field, you can't also specify the logStreamNamePrefixes field.

You can specify this parameter only if you specify only one log group in logGroupIdentifiers.

StartLiveTailCommand Output

See StartLiveTailCommandOutput for details

Parameter
Type
Description
$metadata
Required
ResponseMetadata
Metadata pertaining to this request.
responseStream
AsyncIterable<StartLiveTailResponseStream> | undefined

An object that includes the stream returned by your request. It can include both log events and exceptions.

Throws

Name
Fault
Details
AccessDeniedException
client

You don't have sufficient permissions to perform this action.

InvalidOperationException
client

The operation is not valid on the specified resource.

InvalidParameterException
client

A parameter is specified incorrectly.

LimitExceededException
client

You have reached the maximum number of resources that can be created.

ResourceNotFoundException
client

The specified resource does not exist.

CloudWatchLogsServiceException
Base exception class for all service exceptions from CloudWatchLogs service.