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CouchBackup

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CouchBackup is a command-line utility that allows a Cloudant or CouchDB database to be backed up to a text file. It comes with a companion command-line utility that can restore the backed up data.

Limitations

Couchbackup has some restrictions in the data it's able to backup:

  • couchbackup does not do CouchDB replication as such, it simply streams through a database's _changes feed, and uses POST /db/_bulk_get to fetch the documents, storing the documents it finds on disk.
  • couchbackup does not support backing up or restoring databases containing documents with attachments. It is recommended to store attachments directly in an object store. DO NOT USE THIS TOOL FOR DATABASES CONTAINING ATTACHMENTS. Note

Installation

To install the latest released version use npm:

npm install -g @cloudant/couchbackup

Requirements

  • The minimum required Node.js version is 10.
  • The minimum required CouchDB version is 2.0.0.

Snapshots

The latest builds of master are published to npm with the snapshot tag. Use the snapshot tag if you want to experiment with an unreleased fix or new function, but please note that snapshot versions are unsupported.

Usage

Either environment variables or command-line options can be used to specify the URL of the CouchDB or Cloudant instance, and the database to work with.

The URL

To define the URL of the CouchDB instance set the COUCH_URL environment variable:

export COUCH_URL=http://localhost:5984

or

export COUCH_URL=https://myusername:[email protected]

Alternatively we can use the --url command-line parameter.

When passing credentials in the user information subcomponent of the URL they must be percent encoded. Specifically, within either the username or password, the characters : / ? # [ ] @ % MUST be precent-encoded, other characters MAY be percent encoded.

For example, for the username user123 and password colon:at@321:

https://user123:colon%3aat%40321@localhost:5984

Note that additional care must be taken to escape shell reserved characters when setting the environment variable or command-line parameter.

The Database name

To define the name of the database to backup or restore, set the COUCH_DATABASE environment variable:

export COUCH_DATABASE=animaldb

Alternatively we can use the --db command-line parameter

Backup

To backup a database to a text file, use the couchbackup command, directing the output to a text file:

couchbackup > backup.txt

Another way of backing up is to set the COUCH_URL environment variable only and supply the database name on the command-line:

couchbackup --db animaldb > animaldb.txt

Logging & resuming backups

You may also create a log file which records the progress of the backup with the --log parameter e.g.

couchbackup --db animaldb --log animaldb.log > animaldb.txt

This log file can be used to resume backups from where you left off with --resume true:

couchbackup --db animaldb --log animaldb.log --resume true >> animaldb.txt

The --resume true option works for a backup that has finished spooling changes, but has not yet completed downloading all the necessary batches of documents. It does not provide an incremental backup solution.

You may also specify the name of the output file, rather than directing the backup data to stdout:

couchbackup --db animaldb --log animaldb.log --resume true --output animaldb.txt

Restore

Now we have our backup text file, we can restore it to an existing database using the couchrestore:

cat animaldb.txt | couchrestore

or specifying the database name on the command-line:

cat animaldb.txt | couchrestore --db animaldb2

Compressed backups

If we want to compress the backup data before storing to disk, we can pipe the contents through gzip:

couchbackup --db animaldb | gzip > animaldb.txt.gz

and restore the file with:

cat animaldb.tar.gz | gunzip | couchdbrestore --db animaldb2

Encrypted backups

Similarly to compression it is possible to pipe the backup content through an encryption or decryption utility. For example with openssl:

couchbackup --db animaldb | openssl aes-128-cbc -pass pass:12345 > encrypted_animal.db
openssl aes-128-cbc -d -in encrypted_animal.db -pass pass:12345 | couchrestore --db animaldb2

Note that the content is unencrypted while it is being processed by the backup tool before it is piped to the encryption utility.

What's in a backup file?

A backup file is a text file where each line contains a JSON encoded array of up to buffer-size objects e.g.

    [{"a":1},{"a":2}...]
    [{"a":501},{"a":502}...]

What's in a log file?

A log file contains a line:

  • for every batch of document ids that need to be fetched e.g. :t batch56 [{"id":"a"},{"id":"b"}]
  • for every batch that has been fetched and stored e.g. :d batch56
  • to indicate that the changes feed was fully consumed e.g. :changes_complete

What is shallow mode?

When you run couchbackup with --mode shallow a simpler backup is performed, only backing up the winning revisions of the database. No revision tokens are saved and any conflicting revisions are ignored. This is a faster, but less complete backup. Shallow backups cannot be resumed because they do not produce a log file.

NOTE: Parallellism will not be in effect if --mode shallow is defined.

Why use CouchBackup?

The easiest way to backup a CouchDB database is to copy the ".couch" file. This is fine on a single-node instance, but when running multi-node Cloudant or using CouchDB 2.0 or greater, the ".couch" file only contains a single shard of data. This utility allows simple backups of CouchDB or Cloudant database using the HTTP API.

This tool can be used to script the backup of your databases. Move the backup and log files to cheap Object Storage so that you have multiple copies of your precious data.

Options reference

Environment variables

  • COUCH_URL - the URL of the CouchDB/Cloudant server e.g. http://127.0.0.1:5984
  • COUCH_DATABASE - the name of the database to act upon e.g. mydb (default test)
  • COUCH_PARALLELISM - the number of HTTP requests to perform in parallel when restoring a backup e.g. 10 (Default 5)
  • COUCH_BUFFER_SIZE - the number of documents fetched and restored at once e.g. 100 (default 500). When using CouchBackup with Cloudant on Transaction Engine COUCH_BUFFER_SIZE must be less than 2000 to avoid bad request errors.
  • COUCH_REQUEST_TIMEOUT - the number of milliseconds to wait for a respose to a HTTP request before retrying the request e.g. 10000 (Default 120000)
  • COUCH_LOG - the file to store logging information during backup
  • COUCH_RESUME - if true, resumes a previous backup from its last known position
  • COUCH_OUTPUT - the file name to store the backup data (defaults to stdout)
  • COUCH_MODE - if shallow, only a superficial backup is done, ignoring conflicts and revision tokens. Defaults to full - a full backup.
  • CLOUDANT_IAM_API_KEY - optional IAM API key to use to access the Cloudant database instead of user information credentials in the URL. The endpoint used to retrieve the token defaults to https://iam.cloud.ibm.com/identity/token, but can be overridden if necessary using the CLOUDANT_IAM_TOKEN_URL environment variable.
  • DEBUG - if set to couchbackup, all debug messages will be sent to stderr during a backup or restore process

Note: These environment variables can only be used with the CLI. When using programmatically the opts dictionary must be used.

Command-line parameters

  • --url - same as COUCH_URL environment variable
  • --db - same as COUCH_DATABASE
  • --parallelism - same as COUCH_PARALLELISM
  • --buffer-size - same as COUCH_BUFFER_SIZE
  • --request-timeout - same as COUCH_REQUEST_TIMEOUT
  • --log - same as COUCH_LOG
  • --resume - same as COUCH_RESUME
  • --output - same as COUCH_OUTPUT
  • --mode - same as COUCH_MODE
  • --iam-api-key - same as CLOUDANT_IAM_API_KEY

Using programmatically

You can use couchbackup programatically. First install couchbackup into your project with npm install --save @cloudant/couchbackup. Then you can import the library into your code:

  const couchbackup = require('@cloudant/couchbackup');

The library exports two main functions:

  1. backup - backup from a database to a writable stream.
  2. restore - restore from a readable stream to a database.

Examples

See the examples folder for example scripts showing how to use the library.

Backup

The backup function takes a source database URL, a stream to write to, backup options and a callback for completion.

backup: function(srcUrl, targetStream, opts, callback) { /* ... */ }

The opts dictionary can contain values which map to a subset of the environment variables defined above. Those related to the source and target locations are not required.

  • parallelism: see COUCH_PARALLELISM.
  • bufferSize: see COUCH_BUFFER_SIZE.
  • requestTimeout: see COUCH_REQUEST_TIMEOUT.
  • log: see COUCH_LOG.
  • resume: see COUCH_RESUME.
  • mode: see COUCH_MODE.
  • iamApiKey: see CLOUDANT_IAM_API_KEY.
  • iamTokenUrl: may be used with iamApiKey to override the default URL for retrieving IAM tokens.

The callback has the standard err, data parameters and is called when the backup completes or fails.

The backup function returns an event emitter. You can subscribe to:

  • changes - when a batch of changes has been written to log stream.
  • written - when a batch of documents has been written to backup stream.
  • finished - emitted once when all documents are backed up.

Backup data to a stream:

couchbackup.backup(
  'https://examples.cloudant.com/animaldb',
  process.stdout,
  {parallelism: 2},
  function(err, data) {
    if (err) {
      console.error("Failed! " + err);
    } else {
      console.error("Success! " + data);
    }
  });

Or to a file:

couchbackup.backup(
  'https://examples.cloudant.com/animaldb',
  fs.createWriteStream(filename),
  {parallelism: 2},
  function(err, data) {
    if (err) {
      console.error("Failed! " + err);
    } else {
      console.error("Success! " + data);
    }
  });

Restore

The restore function takes a readable stream containing the data emitted by the backup function. It uploads that to a Cloudant database, which should be a new database.

restore: function(srcStream, targetUrl, opts, callback) { /* ... */ }

The opts dictionary can contain values which map to a subset of the environment variables defined above. Those related to the source and target locations are not required.

  • parallelism: see COUCH_PARALLELISM.
  • bufferSize: see COUCH_BUFFER_SIZE.
  • requestTimeout: see COUCH_REQUEST_TIMEOUT.
  • iamApiKey: see CLOUDANT_IAM_API_KEY.
  • iamTokenUrl: may be used with iamApiKey to override the default URL for retrieving IAM tokens.

The callback has the standard err, data parameters and is called when the restore completes or fails.

The restore function returns an event emitter. You can subscribe to:

  • restored - when a batch of documents is restored.
  • finished - emitted once when all documents are restored.

The backup file (or srcStream) contains lists comprising of document revisions, where each list is separated by a newline. The list length is dictated by the bufferSize parameter used during the backup.

It's possible a list could be corrupt due to failures in the backup process. A BackupFileJsonError is emitted for each corrupt list found. These can only be ignored if the backup that generated the stream did complete successfully. This ensures that corrupt lists also have a valid counterpart within the stream.

Restore data from a stream:

couchbackup.restore(
  process.stdin,
  'https://examples.cloudant.com/new-animaldb',
  {parallelism: 2},
  function(err, data) {
    if (err) {
      console.error("Failed! " + err);
    } else {
      console.error("Success! " + data);
    }
  });

Or from a file:

couchbackup.restore(
  fs.createReadStream(filename),
  'https://examples.cloudant.com/new-animaldb',
  {parallelism: 2},
  function(err, data) {
    if (err) {
      console.error("Failed! " + err);
    } else {
      console.error("Success! " + data);
    }
  });

Error Handling

The couchbackup and couchrestore processes are designed to be relatively robust over an unreliable network. Work is batched and any failed requests are retried indefinitely. However, certain aspects of the execution will not tolerate failure:

  • Spooling changes from the database changes feed. A failure in the changes request during the backup process will result in process termination.
  • Validating the existence of a target database during the database restore process.

API

When using the library programmatically an Error will be passed in one of two ways:

  • For fatal errors the callback will be called with null, error arguments
  • For non-fatal errors an error event will be emitted

CLI Exit Codes

On fatal errors, couchbackup and couchrestore will exit with non-zero exit codes. This section details them.

common to both couchbackup and couchrestore

  • 1: unknown CLI option or generic error.
  • 2: invalid CLI option.
  • 10: backup source or restore target database does not exist.
  • 11: unauthorized credentials for the database.
  • 12: incorrect permissions for the database.
  • 40: database returned a fatal HTTP error.

couchbackup

  • 20: resume was specified without a log file.
  • 21: the resume log file does not exist.
  • 22: incomplete changes in log file.
  • 30: error spooling changes from the database.
  • 50: source database does not support /_bulk_get endpoint.

couchrestore

Note on attachments

TLDR; If you backup a database that contains attachments you will not be able to restore it.

As documented above couchbackup does not support backing up or restoring databases containing documents with attachments. Attempting to backup a database that includes documents with attachments will appear to succeed. However, the attachment content will not have been downloaded and the backup file will contain attachment metadata. Consequently any attempt to restore the backup will result in errors because the attachment metadata will reference attachments that are not present in the restored database.

It is recommended to store attachments directly in an object store with a link in the JSON document instead of using the native attachment API.