This page describes how Cloud Storage tools retry failed requests and how to customize the behavior of retries. It also describes considerations for retrying requests.
Overview
There are two factors that determine whether or not a request is safe to retry:
- The response that you receive from the request.
- The idempotency of the request.
Response
The response that you receive from your request indicates whether or not it's useful to retry the request. Responses related to transient problems are generally retryable. On the other hand, response related to permanent errors indicate you need to make changes, such as authorization or configuration changes, before it's useful to try the request again. The following responses indicate transient problems that are useful to retry:
- HTTP
408
,429
, and5xx
response codes. - Socket timeouts and TCP disconnects.
For more information, see the status and error codes for JSON and XML.
Idempotency
A request that is idempotent means it can be performed repeatedly and always leaves the targeted resource in the same end state. For example, listing requests are always idempotent, because such requests do not modify resources. On the other hand, creating a new Pub/Sub notification is never idempotent, because it creates a new notification ID each time the request succeeds.
The following are examples of conditions that make an operation idempotent:
The operation has the same observable effect on the targeted resource even when continually requested.
The operation only succeeds once.
The operation has no observable effect on the state of the targeted resource.
When you receive a retryable response, you should consider the idempotency of the request, because retrying requests that are not idempotent can lead to race conditions and other conflicts.
Conditional idempotency
A subset of requests are conditionally idempotent, which means they are only idempotent if they include specific optional arguments. Operations that are conditionally safe to retry should only be retried by default if the condition case passes. Cloud Storage accepts preconditions and ETags as condition cases for requests.
Idempotency of operations
The following table lists the Cloud Storage operations that fall into each category of idempotency.
Idempotency | Operations |
---|---|
Always idempotent |
|
Conditionally idempotent |
|
Never idempotent |
|
1This field is available for use in the JSON API. For fields available for use in the client libraries, see the relevant client library documentation.
How Cloud Storage tools implement retry strategies
Console
The Google Cloud console sends requests to Cloud Storage on your behalf and handles any necessary backoff.
Command line
gcloud storage
commands retry the errors listed in
the Response section without requiring you to take additional action.
You might have to take action for other errors, such as the following:
Invalid credentials or insufficient permissions.
Network unreachable because of a proxy configuration problem.
For retryable errors, the gcloud CLI retries requests using a truncated binary exponential backoff strategy. The default number of maximum retries is 32 for the gcloud CLI.
Client libraries
C++
By default, operations support retries for the following HTTP error codes, as well as any socket errors that indicate the connection was lost or never successfully established.
408 Request Timeout
429 Too Many Requests
500 Internal Server Error
502 Bad Gateway
503 Service Unavailable
504 Gateway Timeout
All exponential backoff and retry settings in the C++ library are configurable. If the algorithms implemented in the library do not support your needs, you can provide custom code to implement your own strategies.
Setting | Default value |
---|---|
Auto retry | True |
Maximum time retrying a request | 15 minutes |
Initial wait (backoff) time | 1 second |
Wait time multiplier per iteration | 2 |
Maximum amount of wait time | 5 minutes |
By default, the C++ library retries all operations with retryable
errors, even those that are never idempotent and can delete or create
multiple resources when repeatedly successful. To only retry idempotent
operations, use the google::cloud::storage::StrictIdempotencyPolicy
class.
C#
The C# client library uses exponential backoff by default.
Go
By default, operations support retries for the following errors:
- Connection errors:
io.ErrUnexpectedEOF
: This may occur due to transient network issues.url.Error
containingconnection refused
: This may occur due to transient network issues.url.Error
containingconnection reset by peer
: This means that Google Cloud has reset the connection.net.ErrClosed
: This means that Google Cloud has closed the connection.
- HTTP codes:
408 Request Timeout
429 Too Many Requests
500 Internal Server Error
502 Bad Gateway
503 Service Unavailable
504 Gateway Timeout
- Errors that implement the
Temporary()
interface and give a value oferr.Temporary() == true
- Any of the above errors that have been wrapped using Go 1.13 error wrapping
All exponential backoff settings in the Go library are configurable. By default, operations in Go use the following settings for exponential backoff (defaults are taken from gax):
Setting | Default value (in seconds) |
---|---|
Auto retry | True if idempotent |
Max number of attempts | No limit |
Initial retry delay | 1 second |
Retry delay multiplier | 2.0 |
Maximum retry delay | 30 seconds |
Total timeout (resumable upload chunk) | 32 seconds |
Total timeout (all other operations) | No limit |
In general, retrying continues indefinitely unless the controlling
context is canceled, the client is closed, or a non-transient error is
received. To stop retries from continuing, use context timeouts or
cancellation. The only exception to this behavior is when performing
resumable uploads using Writer, where the data is
large enough that it requires multiple requests. In this scenario, each
chunk times out and stops retrying after 32 seconds by default. You can
adjust the default timeout by changing Writer.ChunkRetryDeadline
.
There is a subset of Go operations that are conditionally idempotent (conditionally safe to retry). These operations only retry if they meet specific conditions:
GenerationMatch
orGeneration
- Safe to retry if a
GenerationMatch
precondition was applied to the call, or ifObjectHandle.Generation
was set.
- Safe to retry if a
MetagenerationMatch
- Safe to retry if a
MetagenerationMatch
precondition was applied to the call.
- Safe to retry if a
Etag
- Safe to retry if the method inserts an
etag
into the JSON request body. Only used inHMACKeyHandle.Update
whenHmacKeyMetadata.Etag
has been set.
- Safe to retry if the method inserts an
RetryPolicy
is set to RetryPolicy.RetryIdempotent
by default. See
Customize retries for examples on how to modify the default retry
behavior.
Java
By default, operations support retries for the following errors:
- Connection errors:
Connection reset by peer
: This means that Google Cloud has reset the connection.Unexpected connection closure
: This means Google Cloud has closed the connection.
- HTTP codes:
408 Request Timeout
429 Too Many Requests
500 Internal Server Error
502 Bad Gateway
503 Service Unavailable
504 Gateway Timeout
All exponential backoff settings in the Java library are configurable. By default, operations through Java use the following settings for exponential backoff:
Setting | Default value (in seconds) |
---|---|
Auto retry | True if idempotent |
Max number of attempts | 6 |
Initial retry delay | 1 second |
Retry delay multiplier | 2.0 |
Maximum retry delay | 32 seconds |
Total Timeout | 50 seconds |
Initial RPC Timeout | 50 seconds |
RPC Timeout Multiplier | 1.0 |
Max RPC Timeout | 50 seconds |
Connect Timeout | 20 seconds |
Read Timeout | 20 seconds |
For more information about the settings, see the Java reference
documentation for RetrySettings.Builder
and
HttpTransportOptions.Builder
.
There is a subset of Java operations that are conditionally idempotent (conditionally safe to retry). These operations only retry if they include specific arguments:
ifGenerationMatch
orgeneration
- Safe to retry if
ifGenerationMatch
orgeneration
was passed in as an option to the method.
- Safe to retry if
ifMetagenerationMatch
- Safe to retry if
ifMetagenerationMatch
was passed in as an option.
- Safe to retry if
StorageOptions.setStorageRetryStrategy
is set to
StorageRetryStrategy#getDefaultStorageRetryStrategy
by default.
See Customize retries for examples on how to modify the default
retry behavior.
Node.js
By default, operations support retries for the following error codes:
- Connection errors:
EAI_again
: This is a DNS lookup error. For more information, see thegetaddrinfo
documentation.Connection reset by peer
: This means that Google Cloud has reset the connection.Unexpected connection closure
: This means Google Cloud has closed the connection.
- HTTP codes:
408 Request Timeout
429 Too Many Requests
500 Internal Server Error
502 Bad Gateway
503 Service Unavailable
504 Gateway Timeout
All exponential backoff settings in the Node.js library are configurable. By default, operations through Node.js use the following settings for exponential backoff:
Setting | Default value (in seconds) |
---|---|
Auto retry | True if idempotent |
Maximum number of retries | 3 |
Initial wait time | 1 second |
Wait time multiplier per iteration | 2 |
Maximum amount of wait time | 64 seconds |
Default deadline | 600 seconds |
There is a subset of Node.js operations that are conditionally idempotent (conditionally safe to retry). These operations only retry if they include specific arguments:
ifGenerationMatch
orgeneration
- Safe to retry if
ifGenerationMatch
orgeneration
was passed in as an option to the method. Often, methods only accept one of these two parameters.
- Safe to retry if
ifMetagenerationMatch
- Safe to retry if
ifMetagenerationMatch
was passed in as an option.
- Safe to retry if
retryOptions.idempotencyStrategy
is set to
IdempotencyStrategy.RetryConditional
by default. See
Customize retries for examples on how to modify the default retry
behavior.
PHP
The PHP client library uses exponential backoff by default.
Python
By default, operations support retries for the following error codes:
- Connection errors:
requests.exceptions.ConnectionError
requests.exceptions.ChunkedEncodingError
(only for operations that fetch or send payload data to objects, like uploads and downloads)ConnectionError
- HTTP codes:
408 Request Timeout
429 Too Many Requests
500 Internal Server Error
502 Bad Gateway
503 Service Unavailable
504 Gateway Timeout
Operations through Python use the following default settings for exponential backoff:
Setting | Default value (in seconds) |
---|---|
Auto retry | True if idempotent |
Initial wait time | 1 |
Wait time multiplier per iteration | 2 |
Maximum amount of wait time | 60 |
Default deadline | 120 |
There is a subset of Python operations that are conditionally idempotent (conditionally safe to retry) when they include specific arguments. These operations only retry if a condition case passes:
DEFAULT_RETRY_IF_GENERATION_SPECIFIED
- Safe to retry if
generation
orif_generation_match
was passed in as an argument to the method. Often methods only accept one of these two parameters.
- Safe to retry if
DEFAULT_RETRY_IF_METAGENERATION_SPECIFIED
- Safe to retry if
if_metageneration_match
was passed in as an argument to the method.
- Safe to retry if
DEFAULT_RETRY_IF_ETAG_IN_JSON
- Safe to retry if the method inserts an
etag
into the JSON request body. ForHMACKeyMetadata.update()
this means etag must be set on theHMACKeyMetadata
object itself. For theset_iam_policy()
method on other classes, this means the etag must be set in the "policy" argument passed into the method.
- Safe to retry if the method inserts an
Ruby
By default, operations support retries for the following error codes:
- Connection errors:
SocketError
HTTPClient::TimeoutError
Errno::ECONNREFUSED
HTTPClient::KeepAliveDisconnected
- HTTP codes:
408 Request Timeout
429 Too Many Requests
5xx Server Error
All exponential backoff settings in the Ruby client library are configurable. By default, operations through the Ruby client library use the following settings for exponential backoff:
Setting | Default value |
---|---|
Auto retry | True |
Max number of retries | 3 |
Initial wait time | 1 second |
Wait time multiplier per iteration | 2 |
Maximum amount of wait time | 60 seconds |
Default deadline | 900 seconds |
There is a subset of Ruby operations that are conditionally idempotent (conditionally safe to retry) when they include specific arguments:
if_generation_match
orgeneration
- Safe to retry if the
generation
orif_generation_match
parameter is passed in as an argument to the method. Often methods only accept one of these two parameters.
- Safe to retry if the
if_metageneration_match
- Safe to retry if the
if_metageneration_match
parameter is passed in as an option.
- Safe to retry if the
By default, all idempotent operations are retried, and conditionally idempotent operations are retried only if the condition case passes. Non-idempotent operations are not retried. See Customize retries for examples on how to modify the default retry behavior.
REST APIs
When calling the JSON or XML API directly, you should use the exponential backoff algorithm to implement your own retry strategy.
Customizing retries
Console
You cannot customize the behavior of retries using the Google Cloud console.
Command line
For gcloud storage
commands, you can control the retry strategy by
creating a named configuration and setting some or all of the
following properties:
base_retry_delay
exponential_sleep_multiplier
max_retries
max_retry_delay
You then apply the defined configuration either on a per-command basis by
using the --configuration
project-wide flag or for all gcloud
commands by using the gcloud config set
command.
Client libraries
C++
To customize the retry behavior, provide values for the following options
when you initialize the google::cloud::storage::Client
object:
google::cloud::storage::RetryPolicyOption
: The library providesgoogle::cloud::storage::LimitedErrorCountRetryPolicy
andgoogle::cloud::storage::LimitedTimeRetryPolicy
classes. You can provide your own class, which must implement thegoogle::cloud::RetryPolicy
interface.google::cloud::storage::BackoffPolicyOption
: The library provides thegoogle::cloud::storage::ExponentialBackoffPolicy
class. You can provide your own class, which must implement thegoogle::cloud::storage::BackoffPolicy
interface.google::cloud::storage::IdempotencyPolicyOption
: The library provides thegoogle::cloud::storage::StrictIdempotencyPolicy
andgoogle::cloud::storage::AlwaysRetryIdempotencyPolicy
classes. You can provide your own class, which must implement thegoogle::cloud::storage::IdempotencyPolicy
interface.
For more information, see the C++ client library reference documentation.
C#
You cannot customize the default retry strategy used by the C# client library.
Go
When you initialize a storage client, a default retry configuration will be set. Unless they're overridden, the options in the config are set to the default values. Users can configure non-default retry behavior for a single library call (using BucketHandle.Retryer and ObjectHandle.Retryer) or for all calls made by a client (using Client.SetRetry). To modify retry behavior, pass in the relevant RetryOptions to one of these methods.
See the following code sample to learn how to customize your retry behavior.
Java
When you initialize Storage
, an instance of
RetrySettings
is initialized as well. Unless they are
overridden, the options in the RetrySettings
are set to the
default values. To modify the default automatic retry behavior, pass
the custom StorageRetryStrategy
into the StorageOptions
used to
construct the Storage
instance. To modify any of the other scalar
parameters, pass a custom RetrySettings
into the StorageOptions
used
to construct the Storage
instance.
See the following example to learn how to customize your retry behavior:
Node.js
When you initialize Cloud Storage, a retryOptions config
file is initialized as well. Unless they're overridden, the options
in the config are set to the default values. To modify the
default retry behavior, pass the custom retry configuration
retryOptions
into the storage constructor upon initialization.
The Node.js client library can automatically use backoff strategies to
retry requests with the autoRetry
parameter.
See the following code sample to learn how to customize your retry behavior.
PHP
You cannot customize the default retry strategy used by the PHP client library.
Python
To modify the default retry behavior, create a copy of the
google.cloud.storage.retry.DEFAULT_RETRY
object by calling it with a
with_XXX
method. The Python client library automatically uses backoff
strategies to retry requests if you include the DEFAULT_RETRY
parameter.
Note that with_predicate
is not supported for operations that fetch or
send payload data to objects, like uploads and downloads. It's
recommended that you modify attributes one by one. For more information,
see the google-api-core Retry reference.
To configure your own conditional retry, create a
ConditionalRetryPolicy
object and wrap your custom Retry
object with DEFAULT_RETRY_IF_GENERATION_SPECIFIED
,
DEFAULT_RETRY_IF_METAGENERATION_SPECIFIED
, or
DEFAULT_RETRY_IF_ETAG_IN_JSON
.
See the following code sample to learn how to customize your retry behavior.
Ruby
When you initialize the storage client, all retry configurations are set to the values shown in the table above. To modify the default retry behavior, pass retry configurations while initializing the storage client.
To override the number of retries for a particular operation, pass
retries
in the options
parameter of the operation.
REST APIs
Use the exponential backoff algorithm to implement your own retry strategy.
Exponential backoff algorithm
An exponential backoff algorithm retries requests using exponentially increasing waiting times between requests, up to a maximum backoff time. You should generally use exponential backoff with jitter to retry requests that meet both the response and idempotency criteria. For best practices implementing automatic retries with exponential backoff, see Addressing Cascading Failures.
What's next
- Learn more about request preconditions.