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最後更新於Dec 17, 2024 | 查看所有文件

Let’s Encrypt provides rate limits to ensure fair usage by as many people as possible. We believe these rate limits are high enough to work for most people by default. We’ve also designed them so that renewing a certificate almost never hits a rate limit, and so that large organizations can gradually increase the number of certificates they can issue without requiring intervention from Let’s Encrypt.

If you’re actively developing or testing a Let’s Encrypt client, please utilize our staging environment instead of the production API. If you’re working on integrating Let’s Encrypt as a provider or with a large website please review our Integration Guide.

How Our Rate Limits Work

Limits are calculated, per request, using a token bucket algorithm. This approach provides flexibility in how you use your allotted requests. You can either make requests in bursts—up to the full limit—or space out your requests to avoid the risk of being limited.

If you’ve hit a rate limit, we don’t have a way to temporarily reset it. Don’t worry, your capacity for that limit will gradually refill over time, allowing you to make more requests without any additional action on your part. Revoking certificates does not reset rate limits, because the resources used to issue those certificates have already been consumed. For more information please see Retrying After Hitting Rate Limits.

Account Registration Limits

The following limits apply when subscribers request a new account using the new-account API endpoint. Exceeding these limits is very rare. We recommend that large integrators prefer a design which uses one account for many customers.

New Registrations per IP Address

Up to 10 accounts can be created from a single IP address every 3 hours. The ability to create new accounts refills at a rate of 1 account every 18 minutes.

Overrides

We do not offer overrides for this limit.

New Registrations per IPv6 Range

Up to 500 accounts can be created from a single /48 IPv6 subnet every 3 hours. The ability to create new accounts refills at a rate of 1 account every 22 seconds.

Overrides

We do not offer overrides for this limit.

Certificate Issuance Limits

The following limits apply when subscribers request a new certificate using the new-order API endpoint. Exceeding these limits is more common, especially for large hosting providers or organizations issuing certificates for many hostnames.

New Orders per Account

Each time you request a certificate from Let’s Encrypt, a new order is created. A single certificate can include up to 100 hostnames. For performance reasons, it’s better to use fewer hostnames per certificate whenever you can.

Limit

Up to 300 new orders can be created by a single account every 3 hours. The ability to create new orders refills at a rate of 1 order every 36 seconds.

Overrides

To exceed this limit, you must request an override for a specific account.

New Certificates per Registered Domain

A registered domain is, generally speaking, the part of the domain you purchased from your domain name registrar. For instance, in www.example.com, the registered domain is example.com. In new.blog.example.co.uk, the registered domain is example.co.uk. We use the Public Suffix List to identify registered domains.

Limit

Up to 50 certificates can be issued per registered domain every 7 days. This is a global limit, and all new order requests, regardless of which account submits them, count towards this limit. The ability to issue new certificates for the same registered domain refills at a rate of 1 certificate every 202 minutes.

Overrides

To exceed this limit, you must request an override for the specific registered domain or an account.

New Certificates per Exact Set of Hostnames

If you request a certificate for example.com and login.example.com, the “exact set of hostnames” is [example.com, login.example.com]. If you request a certificate for only 1 hostname, such as example.co.uk, then the exact set of hostnames would be [example.co.uk].

Limit

Up to 5 certificates can be issued per exact same set of hostnames every 7 days. This is a global limit, and all new order requests, regardless of which account submits them, count towards this limit. The ability to request new certificates for the same exact set of hostnames refills at a rate of 1 certificate every 34 hours.

Common Causes

Reinstalling your client multiple times to troubleshoot an unknown error, or deleting your ACME client’s configuration data each time you deploy your application, are common ways to hit this limit. We have intentionally set this limit relatively low to prevent buggy systems or software under development from rapidly consuming the capacity of other rate limits.

When testing or troubleshooting your applications, we recommend configuring your client to use our staging environment, which has significantly higher limits.

Workaround

If you’ve hit this limit, you can change the set of hostnames by adding blog.example.com, to request additional certificates. Be aware that these new orders would not be considered renewals. Therefore, they would be subject to the New Orders per Account and New Certificates per Registered Domain rate limits.

Overrides

We do not offer overrides for this limit.

Authorization Failures per Hostname per Account

An authorization is generated for each hostname included in an order. Before a certificate can be issued, all authorizations in the order must be successfully validated. A failed authorization means that, although the requests for validation were sent successfully, all attempts by Let’s Encrypt to validate control of the hostname have failed.

Limit

Up to 5 authorization failures per hostname can be incurred by one account every hour. The ability to incur authorization failures refills at a rate of 1 per hostname every 12 minutes. Once exceeded, this limit is enforced by preventing any new orders for the same hostname, by the same account until the limit resets.

Common Causes

Before you begin troubleshooting, we recommend you set your client to use our staging environment. This environment has significantly higher limits, which can help you identify and resolve issues without consuming your production limits.

Validation failures when using the HTTP-01 and TLS-ALPN-01 methods usually stem from network or firewall configurations that prevent Let’s Encrypt validation servers from reaching your server.
Validation failures when using the DNS-01 method often result from missed steps or typos during the initial setup process. Typically, this validation method requires you to create a CNAME record in your main DNS zone, enabling your client to set the necessary DNS records during the validation process.

Overrides

We do not offer overrides for this limit.

Consecutive Authorization Failures per Hostname per Account

Similar to Authorization Failures per Hostname per Account but only applies to consecutive failures. This limit is designed to prevent clients from getting stuck forever in a loop of failed validations.

Limit

Up to 3,600 consecutive authorization failures per hostname can be incurred by one account. The ability to incur authorization failures refills at a rate of 1 per hostname every day and resets to zero if an authorization for that hostname is successfully validated. Once exceeded, the account is prevented from requesting new certificates for that hostname. Each time the subscriber attempts to request a certificate they will receive an error containing a link to our Self-Service Portal where they can unpause issuance for the paused hostname and up to 49,999 additional paused hostnames associated with their account.

Failures per Day	Time to Pause
1	∞ (never paused)
2	3,600 days (9.86 years)
5	900 days (2.46 years)
10	400 days (1.10 years)
15	257 days (8.45 months)
20	189 days (6.22 months)
30	124 days (4.08 months)
40	92 days (3.03 months)
120	30 days

Common Causes

Validation failures when using the HTTP-01 and TLS-ALPN-01 methods usually stem from network or firewall configurations that prevent Let’s Encrypt validation servers from reaching your server.
Validation failures when using the DNS-01 method often result from missed steps or typos during the initial setup process. Typically, this validation method requires you to create a CNAME record in your main DNS zone, enabling your client to set the necessary DNS records during the validation process.

Overrides

We do not offer overrides for this limit.

Overall Requests Limit

In addition to our account registration and certificate issuance limits, there are per-endpoint overall request limits that apply per-IP address. These are enforced by our load balancers and are designed to protect the ACME API from being overwhelmed by clients that make too many requests at once.

Endpoint	Requests per IP (per second)	Burst Capacity
/acme/new-nonce	20	10
/acme/new-account	5	15
/acme/new-order	300	200
/acme/revoke-cert	10	100
/acme/renewal-info	1000	100
/acme/*	250	125
/directory	40	N/A

Subscribers who exceed these limits will receive a 503 Service Unavailable HTTP response code. The response will include a Retry-After header.

Limit Exemptions for Renewals

Let’s Encrypt recognizes a new certificate order as a “renewal” in two ways: the preferred method is through ACME Renewal Info (ARI), which is exempt from all rate limits, and the other relies on older renewal detection logic that considers orders with the exact same set of hostnames as renewals but may still be subject to certain rate limits.

ARI Renewals

Renewals coordinated by ARI offer the unique benefit of being exempt from all rate limits. Clients that support ARI periodically check with Let’s Encrypt servers to determine if your existing certificate should be renewed. When the optimal renewal window is reached the client requests a new order explicitly indicating the certificate it replaces. If the new order includes at least one hostname matching the certificate it intends to replace and the certificate has not been previously replaced using ARI, the order will not be subject to any rate limits.

Non-ARI Renewals

If your client or hosting provider has yet to add support for ARI, your order can still be considered a renewal of an earlier certificate if it contains the exact same set of hostnames, ignoring capitalization and the order of hostnames. For example, if you requested a certificate for the hostnames [www.example.com, example.com], you could request four more certificates for [www.example.com, example.com] before hitting the New Certificates per Exact Set of Hostnames rate limit. Each of these new orders would be considered renewals and would be exempt from the New Orders per Account and New Certificates per Registered Domain rate limits. However, unlike ARI renewals, these orders would still be subject to Authorization Failures per Hostname per Account and New Certificates per Exact Set of Hostnames.

Retrying After Hitting Rate Limits

All of our rate limit error messages follow the same format. For example:

too many new registrations (10) from this IP address in the last 3h0m0s,
retry after 1970-01-01 00:18:15 UTC.

You should be able to successfully make the same request after the provided date and time. If your request exceeds the capacity of more than one of our limits, we will always return the error message for the limit that resets furthest in the future.

Retry-After Header

We include a Retry-After header in all rate limit error responses, indicating the duration your client should wait before retrying.

You can get a list of certificates issued for your registered domain by searching crt.sh or Censys, which use the public Certificate Transparency logs.

Requesting an Override

If you are a large hosting provider or organization working on a Let’s Encrypt integration, we have a rate limiting form that can be used to request higher rate limits. It takes a few weeks to process requests, so this form is not suitable if you just need to reset a rate limit faster than it resets on its own.