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* action page * change all page_title fields * update title * constraint through migrate pages * update page title and heading to use sentence case * fix front matter description * Apply suggestions from code review Co-authored-by: Jeff Boruszak <104028618+boruszak@users.noreply.github.com> --------- Co-authored-by: Jeff Boruszak <104028618+boruszak@users.noreply.github.com>
99 lines
3.9 KiB
Plaintext
99 lines
3.9 KiB
Plaintext
---
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layout: docs
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page_title: logs block in the job specification
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description: |-
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Configure a task's log rotation policy in the `logs` block of the Nomad job specification. Set the maximum number of rotated files and the maximum size of each rotated file. Turn off log collection for a task. Review default log rotation values.
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---
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# `logs` block in the job specification
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<Placement groups={['job', 'group', 'task', 'logs']} />
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The `logs` block configures the log rotation policy for a task's `stdout` and
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`stderr`. Logging is enabled by default with reasonable defaults (provided in
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the parameters section below). The `logs` block allows for finer-grained control
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over how Nomad handles log files.
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Nomad's log rotation works by writing stdout/stderr output from tasks to a file
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inside the `alloc/logs/` directory with the following format:
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`<task-name>.<stdout/stderr>.<index>`. Output is written to a particular index,
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starting at zero, till that log file hits the configured `max_file_size`. After,
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a new file is created at `index + 1` and logs will then be written there. A log
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file is never rolled over, instead Nomad will keep up to `max_files` worth of
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logs and once that is exceeded, the log file with the lowest index is deleted.
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```hcl
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job "docs" {
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group "example" {
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task "server" {
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logs {
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max_files = 10
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max_file_size = 10
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disabled = false
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}
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}
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}
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}
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```
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Each job's logs will be written to ephemeral disk space. If you increase the total
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amount of logs on disk, you may want to increase ephemeral disk size as well. See
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the [ephemeral disk documentation][] for more information.
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For information on how to interact with logs after they have been configured,
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please see the [`nomad alloc logs`][logs-command] command.
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## Parameters
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- `max_files` `(int: 10)` - Specifies the maximum number of rotated files Nomad
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will retain for `stdout` and `stderr`. Each stream is tracked individually, so
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specifying a value of 2 will create 4 files - 2 for stdout and 2 for stderr
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- `max_file_size` `(int: 10)` - Specifies the maximum size of each rotated file
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in `MB`. If the amount of disk resource requested for the task is less than
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the total amount of disk space needed to retain the rotated set of files,
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Nomad will return a validation error when a job is submitted.
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- `disabled` `(bool: false)` - Specifies that log collection should be enabled for
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this task. If set to `true`, the task driver will attach stdout/stderr of the
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task to `/dev/null` (or `NUL` on Windows). You should only disable log
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collection if your application has some other way of emitting logs, such as
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writing to a remote syslog server. Note that the `nomad alloc logs` command
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and related APIs will return errors (404 "not found") if logging is disabled.
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Some task drivers such as `docker` support a [`disable_log_collection`][]
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option. If the task driver's `disable_log_collection` option is set to `true`,
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it will override `disabled=false` in the task's `logs` block.
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## Examples
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The following examples only show the `logs` blocks. Remember that the
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`logs` block is only valid in the placements listed above.
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### Configure defaults
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This example shows a default logging configuration. Yes, it is empty on purpose.
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Nomad automatically enables logging with reasonable defaults as described in the
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parameters section above.
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```hcl
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```
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### Customization
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This example asks Nomad to retain 3 rotated files for each of `stderr` and
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`stdout`, each a maximum size of 5 MB per file. The minimum disk space this
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would require is 30 MB (3 `stderr` + 3 `stdout` × 5 MB = 30 MB).
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```hcl
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logs {
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max_files = 3
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max_file_size = 5
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}
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```
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[logs-command]: /nomad/docs/commands/alloc/logs 'Nomad logs command'
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[`disable_log_collection`]: /nomad/docs/drivers/docker#disable_log_collection
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[ephemeral disk documentation]: /nomad/docs/job-specification/ephemeral_disk 'Nomad ephemeral disk Job Specification'
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