apache/dolphinscheduler · error · ServiceException

task instance is null or host is null

Error message

task instance is null or host is null

What it means

getLogBytes looks up the task instance by id and requires both the instance to exist and its host to be non-blank, because log bytes are fetched from the worker host. If the instance is missing or its host is empty, a ServiceException with the literal message 'task instance is null or host is null' is thrown instead of a typed status.

Source

Thrown at dolphinscheduler-api/src/main/java/org/apache/dolphinscheduler/api/service/impl/LoggerServiceImpl.java:113

        Result<ResponseTaskLog> result = new Result<>(Status.SUCCESS.getCode(), Status.SUCCESS.getMsg());
        String log = queryLog(taskInstance, skipLineNum, limit);
        int lineNum = log.split("\\r\\n").length;
        result.setData(new ResponseTaskLog(lineNum, log));
        return result;
    }

    /**
     * get log size
     *
     * @param loginUser  login user
     * @param taskInstId task instance id
     * @return log byte array
     */
    @Override
    public byte[] getLogBytes(User loginUser, int taskInstId) {
        TaskInstance taskInstance = taskInstanceDao.queryById(taskInstId);
        if (taskInstance == null || StringUtils.isBlank(taskInstance.getHost())) {
            throw new ServiceException("task instance is null or host is null");
        }
        Project project = projectDao.queryProjectByTaskInstanceId(taskInstId);
        projectService.checkProjectAndAuthThrowException(loginUser, project, DOWNLOAD_LOG);
        return getLogBytes(taskInstance);
    }

    /**
     * query log
     *
     * @param loginUser   login user
     * @param projectCode project code
     * @param taskInstId  task instance id
     * @param skipLineNum skip line number
     * @param limit       limit
     * @return log string data
     */
    @Override
    @SuppressWarnings("unchecked")

View on GitHub (pinned to 02eac45a1b)

Solutions

1. Confirm taskInstId exists: query t_ds_task_instance for that id before downloading.
2. Wait until the task has been dispatched and has a non-empty host; retry after the task starts running.
3. Download logs from a completed, assigned task instance instead.
4. If hosts are legitimately blank due to DB corruption, re-run the task to regenerate host info.

Example fix

// before: blind download
service.getLogBytes(loginUser, 999999);
// after: guard first
TaskInstance ti = taskInstanceDao.queryById(999999);
if (ti == null || StringUtils.isBlank(ti.getHost())) {
    throw new ServiceException(Status.TASK_INSTANCE_NOT_FOUND);
}
service.getLogBytes(loginUser, 999999);

TaskInstance ti = taskInstanceDao.queryById(taskInstId);
if (ti == null || StringUtils.isBlank(ti.getHost())) {
    throw new ServiceException(Status.TASK_INSTANCE_NOT_FOUND);
}

boolean isDownloadable(TaskInstance ti) { return ti != null && StringUtils.isNotBlank(ti.getHost()); }

try {
    byte[] log = loggerService.getLogBytes(loginUser, taskInstId);
} catch (ServiceException e) {
    if (e.getMessage() != null && e.getMessage().contains("task instance is null")) {
        // inform user the task has not run on any worker yet / does not exist
    } else { throw e; }
}

When it happens

Trigger: Calling GET /log/download-log (or getLogBytes) with a taskInstId that does not exist, or whose task instance has an empty host (task not yet dispatched to a worker, or host data lost).

Common situations: Downloading logs for a task that failed before being assigned to a worker; requesting logs of a task instance deleted from the DB; stale UI link pointing at a purged instance id.

Understand the failure class

Background: Record Not Found Errors: "not found", RecordNotFound, and "was not found" — what they mean and how to fix them — this error's family across 28 libraries.

Related errors

• TASK_INSTANCE_NOT_FOUND
• 10103
• The task instance is not under the project: {projectCode}
• The workflow instance is not finished: {workflowInstanceStat
• 10165

AI-assisted analysis of apache/dolphinscheduler@02eac45a1b (2026-09-06). Data as JSON: /api/errors/c95c6ab0f27a6dda. Report an issue: GitHub.