slave-extras.md

Singularity Extras for Mesos Slaves

This document assumes you've already followed the steps from install.md

• SingularityExecutor, a custom Mesos executor. This executor provides numerous benefits over the default Mesos executor, including:
  • Thread usage limits
  • Detailed status updates for tasks
  • Log rotation
  • Support for downloading multiple artifacts
  • "Embedded" artifacts (artifacts bundled into the Task object, as opposed to downloaded)
  • Log persistence in S3 (when used in conjunction with SingularityS3Uploader)
• SingularityExecutorCleanup, a background job that cleans up tasks that haven't cleanly terminated (i.e. have been OOM killed by OS, or the executor experiences a fatal error)
• SingularityS3Uploader, a local service that uploads task logs to S3
• SingularityS3Downloader, a local service that allows the executor to efficiently download files without being subject to OOM kills due to filling up the page cache.

1. Create base property config files.

/etc/singularity.base.yaml -- properties used by all Singularity slave helpers.

# Metadata folder for SingularityS3Uploader
s3UploaderMetadataDirectory: path/to/s3/metadata

# Metadata folder for SingularityLogWatcher
logWatcherMetadataDirectory: path/to/logwatcher/metadata

# Path to write singularity-executor.log
loggingDirectory: path/to/logs

# Desired logging level
loggingLevel:
   com.hubspot: INFO

---

/etc/singularity.s3base.yaml -- properties used by jobs that hit S3.

# AWS S3 access key
s3AccessKey: blah

# AWS S3 secret key
s3SecretKey: secret

# Folder to cache downloaded artifacts in
artifactCacheDirectory: path/to/slugs

2. Install SingularityExecutor

2a. Create a /etc/singularity.executor.yaml file on each slave:

# Folder to store task metadata in (used by SingularityExecutorCleanup)
globalTaskDefinitionDirectory: path/to/tasks

# Default user to run tasks as
defaultRunAsUser: root

# Folder to store rotated logs
logrotateToDirectory: logs

# AWS S3 bucket name
s3UploaderBucket: bucket-name

# Filename format to use when uploading logs to S3
s3UploaderKeyPattern: "%requestId/%Y/%m/%taskId_%index-%s%fileext"

# Additional files to logrotate
logrotateAdditionalFiles:
- logs/access.log
- logs/gc.log

# Path to logrotate command
logrotateCommand: /usr/sbin/logrotate

# Whether or not to use the SingularityS3Downloader service to download artifacts
useLocalDownloadService: true

2b. Store the SingularityExecutor JAR in a well-known place on each slave.

2c. Create a shell script to start the executor on each slave.

/usr/local/bin/singularity-executor:

#!/bin/bash

exec java -Djava.library.path=/usr/local/lib -jar path/to/SingularityExecutor-*-shaded.jar

2d. Update Singularity configuration to allocate resources for custom executors.

When launching Mesos tasks with a custom executor (i.e. SingularityExecutor), you must allocate additional resources to the executor process. Custom executor resources can be set via the customExecutor field:

customExecutor:
  memoryMb: 128
  numCpus: 0.1

This snippet will make Singularity launch tasks with an additional 128 MB of memory and 0.1 CPU devoted solely to the executor.

(This is not necessary if you're not using custom executors -- Mesos will automatically pad your resources to accommodate the default executor.)

3. Install SingularityExecutorCleanup (optional)

3a. Create an /etc/singularity.executor.cleanup.yaml file on each slave.

# Path to store executor cleanup results
executorCleanupResultsDirectory: path/to/cleanup

# Singularity connection string
singularityHosts:
- host:port
- host:port

# URL path to singularity API
singularityContextPath: singularity/api

3b. Store the SingularityExecutorCleanup JAR in a well-known place on each slave.

3c. Create a shell script to start the executor cleanup job on each slave.

/usr/local/bin/singularity-executor-cleanup:

#!/bin/bash

exec java -jar path/to/SingularityExecutorCleanup-*-shaded.jar

3d. Add a crontab entry to run the SingularityExecutorCleanup JAR hourly.

0 * * * * root /usr/local/bin/singularity-executor-cleanup > /dev/null 2>&1

4. Install SingularityS3Downloader (optional)

4a. Store the SingularityS3Downloader JAR in a well-known place on each slave.

4b. Create a shell script to start the S3 downloader service on each slave.

/usr/local/bin/singularity-s3-downloader:

#!/bin/bash

exec java -jar path/to/SingularityS3Downloader-*-shaded.jar

4c. Start the SingularityS3Downloader service.

Consider using a tool like monit, supervisor, or systemd to ensure the service stays running.

5. Install SingularityS3Uploader (optional)

5a. Create an /etc/singularity.s3uploader.yaml file on each slave.

Note: This file only needed if you need to override the access/secret keys from singularity.s3base.yaml.

# AWS S3 access key
s3AccessKey: blah

# AWS S3 secret key
s3SecretKey: secret

5b. Store the SingularityS3Uploader JAR in a well-known place on each slave.

5c. Create a shell script to start the S3 uploader service on each slave.

/usr/local/bin/singularity-s3-uploader:

#!/bin/bash

exec java -jar path/to/SingularityS3Uploader-*-shaded.jar

5d. Start the SingularityS3Uploader service.

Consider using a tool like monit, supervisor, or systemd to ensure the service stays running.