{"id":4305,"date":"2026-05-05T10:11:24","date_gmt":"2026-05-05T10:11:24","guid":{"rendered":"https:\/\/cheapsslweb.com\/blog\/?p=4305"},"modified":"2026-06-16T10:13:58","modified_gmt":"2026-06-16T10:13:58","slug":"acme-challenges-for-domain-validation-which-is-best","status":"publish","type":"post","link":"https:\/\/cheapsslweb.com\/blog\/acme-challenges-for-domain-validation-which-is-best\/","title":{"rendered":"ACME Challenges for Domain Validation: Which is Best?"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">The validation method selected when issuing SSL\/TLS certificates through the <a href=\"https:\/\/cheapsslweb.com\/blog\/what-is-acme-importance-of-automated-certificate-management\/\">ACME protocol<\/a> is critical for achieving a seamless automation process and successfully deploying certificates.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">There are two main challenge types under ACME (HTTP-01 and DNS-01), and while both verify domain control, they do so in very different ways.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What are ACME Challenges?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">ACME challenges are methods used by the Automated Certificate Management Environment (ACME) protocol to verify domain control <span style=\"box-sizing: border-box; margin: 0px; padding: 0px;\">and prove ownership of a domain before an&nbsp;<a href=\"https:\/\/cheapsslweb.com\/\" target=\"_blank\">SSL\/TLS certificate<\/a> is issued<\/span>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">ACME was defined by the Internet Engineering Task Force in RFC 8555, and allows certification authorities (CAs), such as <a href=\"https:\/\/cheapsslweb.com\/ssl-brands\/digicert\">DigiCert<\/a>, <a href=\"https:\/\/cheapsslweb.com\/ssl-brands\/sectigo\">Sectigo<\/a>, and Let\u2019s Encrypt, to automate the issuance and renewal of certificates.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The specific type of challenge requires the owner of a domain to perform a validation task (for example, creating a DNS record or placing a file on a web server) so that the CA can validate that they own the respective domain.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><strong>There are 3 types of ACME Challenges:<\/strong><\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li>HTTP-01 Challenge (HTTP Practical Demonstration DCV)<\/li>\n\n\n\n<li>DNS-01 Challenge (DNS TXT record DCV)<\/li>\n\n\n\n<li>TLS-ALPN-01 Challenge (rarely used)<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">What is the HTTP-01 Challenge?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The HTTP-01 challenge is a method of validating ownership of a domain for ACME certificates by placing a unique token in a publicly accessible place on the web server, typically in the <strong><em>\/.well-known\/acme-challenge\/ directory<\/em><\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The certificate authority will now access this file using HTTP (over <a href=\"https:\/\/cheapsslweb.com\/blog\/port-80-http-vs-port-443-https-major-difference-to-know\/\">TCP port 80<\/a>) to verify control of the domain. The HTTP-01 method is also one of the fastest and easiest DC\/DS-031 validation methods available for automating the HTTP-01 challenge via ACME clients, and is generally available for hosting on standard hosting platforms.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Benefits of the HTTP-01 Challenge<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Simple to Implement<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The relative simplicity of deploying the HTTP-01 challenge method is one of the major reasons why most ACME clients have built-in file creation and deletion support (i.e., when set up correctly).<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">Once the environment has been set up correctly, the validation process will typically take place with minimal user interaction, which is particularly well-suited for simple web hosting solutions.<\/p>\n<\/blockquote>\n\n\n\n<h3 class=\"wp-block-heading\">Fast Validation<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The certificate authorities verify the challenge directly via HTTP (over TCP port 80), and usually complete the validation process within a matter of minutes.<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">Furthermore, if the domain is validated using the HTTP-01 challenge, it does not depend on DNS propagation, which results in significantly faster issuance and renewal of certificates.<\/p>\n<\/blockquote>\n\n\n\n<h3 class=\"wp-block-heading\">Ideal for Standard Web Servers<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">HTTP-01 is ideal for traditional hosting where there is a public web server already set up. If you have a domain that points to a publicly accessible web server, implementing the HTTP-01 challenge is typically very simple and easy to do.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Lower Credentials Risk When Compared to DNS Automation<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Unlike DNS-01, HTTP-01 does not require you to store any DNS API credentials, which reduces the risk of credential exposure and allows you to avoid managing access to the DNS Provider API.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Most ACME Clients Automatically Configure HTTP-01<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Most common ACME clients will automatically configure the required <strong>\/.well-known\/acme-challenge\/<\/strong> path and place the correct token automatically for you. <\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">This is why HTTP-01 is generally a great choice for small businesses and administrators looking for a configuration method with the least amount of functionality to configure.<\/p>\n<\/blockquote>\n\n\n\n<h2 class=\"wp-block-heading\">Limitations of HTTP-01<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Requires Availability on Port 80<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The HTTP-01 validation process will fail if your firewall (or other infrastructure) is blocking communication on TCP <a href=\"https:\/\/cheapsslweb.com\/blog\/what-is-port-80-common-security-risks-associated-with-port-80-http\/\">Port 80<\/a>; additional configuration must be performed to allow for the successful validation test.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Does not support Wildcard Certificates<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The HTTP-01 validation process can only be completed with a publicly routable domain name (to which an FQDN points) as a target.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Therefore, organizations seeking bulk <a href=\"https:\/\/cheapsslweb.com\/ssl-types\/cheap-wildcard-ssl-certificates\">purchase of wildcard certificates<\/a> (e.g., *.example.com) will need to use DNS-01 instead, thus prohibiting use of HTTP-01 by some enterprise or SaaS users.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Not suitable for Non-public Servers<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Load-balanced or reverse-proxy type web servers do not have a publicly routable address and cannot receive any requests directly via HTTP, and will therefore likewise not be able to pass validation if they are using HTTP-01 for validation.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">ACME doesn&#8217;t validate IP Addresses for DV<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">HTTP-01 cannot be used to validate an A record associated with an IP address for Certificate Authority issuance of a DV Certificate using ACME Technology.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Therefore, this restricts the manner in which this technology can be utilized by customers who need to issue certificates based only on compliance with the regulations established by the <a href=\"https:\/\/cheapsslweb.com\/blog\/what-is-acme-importance-of-automated-certificate-management\/\">ACME protocol<\/a>.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Limited Flexibility in Complex Environments<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">As services become distributed or containerized, establishing and maintaining persistent HTTP paths that result in a successful validation can be difficult, limiting HTTP-01&#8217;s effectiveness within advanced infrastructure implementations.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What is the DNS-01 Challenge?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The challenge with DNS-01 is that it verifies domain ownership using an ACME (Automated Certificate Management Environment) domain validation and requires the person who owns the domain to create and publish a TXT record in their DNS settings containing a token generated by the certificate authority.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The CA verifies domain ownership by checking the DNS for that particular record rather than checking the web server.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Because this method does not rely on checking the web server, it works for <a href=\"https:\/\/cheapsslweb.com\/comodo-positivessl-wildcard\">wildcard certificates<\/a>, even if the web server does not have a publicly accessible IP address.<\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">Many certificate authorities, including DigiCert, Let&#8217;s Encrypt, Cloudflare, and GoDaddy, support the DNS-01 challenge, so organizations with infrastructure hosted in cloud, load-balanced, or security-restricted environments benefit from this challenge because it can be automated using the API of the DNS provider.<\/p>\n<\/blockquote>\n\n\n\n<h2 class=\"wp-block-heading\">Advantages of DNS-01<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Supports Wildcard SSL Certificates<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The DNS-01 challenge is the only ACME challenge type that supports <a href=\"https:\/\/cheapsslweb.com\/ssl-types\/cheap-wildcard-ssl-certificates\">wildcard SSL certificates<\/a> (e.g. *.example.com).<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">For organizations looking to secure multiple or dynamic subdomains under a single certificate, especially those that are using SaaS (Software as a Service), enterprise, or multi-tenant environments.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Thus, relying on a wildcard certificate may be the only viable way to achieve the desired level of security.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Doesn&#8217;t require a publicly accessible Web Server<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The DNS-01 challenge does not require access to a publicly accessible web server or <span style=\"box-sizing: border-box; margin: 0px; padding: 0px;\"><a href=\"https:\/\/cheapsslweb.com\/blog\/what-is-port-80-common-security-risks-associated-with-port-80-http\/\" target=\"_blank\">port 80<\/a>, unlike<\/span> the HTTP-01 challenge.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Because the challenge is validated through DNS rather than a web server, it can be validated regardless of whether the infrastructure is behind a firewall, load balancer, or on a private network.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Centralized Domain Validation Control<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Organizations can centralize certificate automation via their DNS provider by managing validation at the DNS layer. This centralization allows organizations to govern certificates in line with multiple domains or large-scale implementations more consistently, better, and at scale.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Enhanced Flexibility for Complex Setups<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">DNS-01 validation works regardless of the hosting provider, server setup, or method of routing user requests.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">By using CDN, reverse proxy, and worldwide systems, DNS-01 validation provides as much flexibility for validating domain names as other methods do, and often more.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Limitations of DNS-01<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Dependent Upon DNS Propagation Time<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Due to its dependence on DNS record propagation, DNS-01 validation may take longer than HTTP-01 validation.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">After creating new or updating existing TXT records, the new record must be propagated to all the global authoritative DNS servers, which may take several minutes or, in some cases, several hours to complete. This propagation may delay certificate issuance.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">More Difficult to Automate<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Unlike HTTP-01, which is typically fully automated at the time of issuance, <strong>DNS-01 validation requires that you have API access to your DNS provider<\/strong> to perform homegrown automated procedures for obtaining issued certificates.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Without having API access to your domain name&#8217;s DNS provider, administrators must perform manual steps to create and remove TXT records, which adds to operational workloads and the capacity for error.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Requires Secure Management of DNS Credentials<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">To automate DNS-01 validation, <strong>users must also securely store and manage their credentials for the DNS API<\/strong>.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">If the credentials are not stored and managed securely or too permissively, there is a potential risk for unauthorized access to the DNS modification for the domain.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Doesn&#8217;t Work Well if You Can\u2019t Control Your Domain\u2019s DNS Settings<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">If you don&#8217;t have direct access or control over your domain&#8217;s DNS settings, like with certain managed hosting or third-party domain providers, it may be challenging to use DNS-01. This limitation also constrains your ability to automate the certification process.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">More Overhead When Using DNS-01 For Small-Scale Sites<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">When you&#8217;re dealing with a straightforward single-domain website, the added complexity of using DNS-01 rather than HTTP-01 may be excessive because it requires you to create new DNS records for each validation instead of using a simple web server-based challenge.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">What is TLS-ALPN-01 ACME Challenge?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">The TLS-ALPN-01 ACME challenge validates domain ownership by requiring the client to present a special self-signed certificate during a TLS handshake on port 443, using the <code>acme-tls\/1<\/code> ALPN protocol identifier. This challenge was developed after TLS-SNI-01 became deprecated, and is being developed as a separate standard. Some ACME clients don&#8217;t support this challenge for validation.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Advantages of TLS-ALPN-01<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Works without Port 80 access<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The value of TLS-ALPN-01 for organisations that have tight firewall rules and are blocking inbound connections on port 80 (HTTP) is very high. Many modern data center environments have purposely disabled HTTP to help diminish the exposure to web-based attack vectors. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">When you use TLS-ALPN-01, the certificate validation occurs completely over <a href=\"https:\/\/cheapsslweb.com\/blog\/port-443-https\/\">port 443<\/a> because the only way to validate your certificate is using the TLS handshake protocol. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This provides a way to continue automated certificate management without having to change your firewall rules or open temporary exceptions that would put your network security at risk.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Maintains a Secure, HTTPS-only Posture<\/h3>\n\n\n\n<ol start=\"2\" class=\"wp-block-list\">\n<li><\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">Because the <a href=\"https:\/\/cheapsslweb.com\/blog\/ssl-tls-handshake-explained-process-work-and-importance\/\">TLS handshake<\/a> is used to validate the certificate authority, all communication between the certificate authority and the web server is encrypted. This is aligned with modern security standards that require HTTPS-only communication between services. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">By comparison, using the HTTP-01 method would cause downtime to your unencrypted endpoint while the validation occurs; using the TLS-ALPN-01 method will not result in a decrease in security, which is why it is an ideal method for organisations with strict compliance and\/or zero trust networking policies.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Independent of Web Server Configuration<\/h3>\n\n\n\n<ol start=\"3\" class=\"wp-block-list\">\n<li><\/li>\n<\/ol>\n\n\n\n<p class=\"wp-block-paragraph\">TLS-ALPN-01 is independent of the web servers because it performs at a lower layer of the network stack &#8211; specifically, during the TLS negotiation &#8211; so it does not depend on the behaviour of the web server (file serving, HTTP request processing). <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This independence eliminates the need for configuring the document root, mapping URL\/URI paths, or redirecting requests. The result is fewer opportunities for possible misconfigurations or unexpected results caused by file location, permission problems, or conflicting web server rules, resulting in a cleaner, more controlled validation process.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Minimises Interference with Application Logic<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Because TLS-ALPN-01 validation occurs before the application layer receives any HTTP requests. Therefore, TLS-ALPN-01 validation does not interfere with or affect any application routing, middleware, or business logic. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This is especially helpful for many applications that have complex routing rules, authentication layers, or API gateways because HTTP-based validation could be impacted by them. This separation means that TLS-ALPN-01 certificate validations can be performed without unintentionally affecting live application traffic.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Suitable for Tightly Controlled Environments<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">In environments characterised as heavily regulated or sensitive in terms of security, like local enterprise, financial or government systems\/networks, services and ports (to connect these services) are typically kept very restricted\/limited. There are usually only a small number of allowed ports\/services. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">TLS-ALPN-01 is a good candidate for this type of environment as it only needs port 443 (which is likely already opened for secure communications). Therefore, organisations can consider using TLS-ALPN-01 for automating their certificate management while still having strict control over how much of their network is exposed, as well as meeting any regulatory requirements they may have.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Useful Fallback when other Methods are not viable<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">TLS-ALPN-01 can be used as an alternative in cases where the more common types of challenges are not usable. <\/p>\n\n\n\n<blockquote class=\"wp-block-quote is-layout-flow wp-block-quote-is-layout-flow\">\n<p class=\"wp-block-paragraph\">For example, when trying to use HTTP-01, and port 80 has been blocked, or when DNS-01 cannot be used due to problems getting access to the DNS API, or simply due to the complexity involved in implementing this solution, TLS-ALPN-01 can be used as a way for automating certificate issuance, even when no other options are available. <\/p>\n<\/blockquote>\n\n\n\n<p class=\"wp-block-paragraph\">However, since TLS-ALPN-01 has much less support than HTTP-01\/DNS-01, it can be more difficult to configure than HTTP-01\/DNS-01. However, at least it means organisations can still automate their certificate management even when other solutions are not viable in their constrained environments.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Limitations of TLS-ALPN-01<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Limited Tool and Platform Support<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">A significant downside to TLS-ALPN-01 is the lack of uptake across ACME clients, hosting providers, and platforms in comparison to HTTP-01 and DNS-01, which have much greater adoption than TLS-ALPN-01. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">As a result, there are very few native implementations supporting TLS-ALPN-01, making it difficult to implement the required challenge. There are many cloud platforms and managed host environments that do not expose TLS-level controls, making it impossible to implement in real-world environments.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Incompatibility with CDN and TLS Termination Setups<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The TLS-ALPN-01 challenge mechanism is not ideal for environments where a CDN, a load balancer, or a reverse proxy terminates TLS before relaying requests onto the origin server, as in this scenario, the intermediary processes the ACME validation request rather than the server for which the challenge response is needed. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Since most CDNs do not support the ALPN protocol (which is required to use the TLS-ALPN-01 challenge), it will not validate properly in a CDN-fronted application; therefore, this challenge type will not work for applications fronted by CDNs.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Higher Implementation Complexity<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">Unlike HTTP-01, which simply requires serving a file, or DNS-01, which consists of updating a DNS record, the TLS-ALPN-01 challenge type requires that TLS connections be dynamically handled according to the TLS handshake specifications. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The <a href=\"https:\/\/cheapsslweb.com\/blog\/ssl-tls-handshake-explained-process-work-and-importance\/\">TLS handshake<\/a> requires the server to present a uniquely created self-signed certificate using the TLS ALPN extension. As a result, it requires deeper integration with the TLS stack and more complicated configurations than HTTP-01 and DNS-01 methods, resulting in greater possibilities for error and longer setup times than the other challenge type.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Requires Control over the TLS Layer<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">The TLS-ALPN-01 challenge type requires that the server can fully control how TLS connections are handled on the server. This level of control is usually not available in most shared hosting or managed environments. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Therefore, if you cannot modify your TLS behaviour or provide a custom certificate for this process during the initial handshake, you simply will not be able to use this challenge type, creating limits to its usage.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">No Support for Wildcard Certificates<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">TLS-ALPN-01 and HTTP-01 (or a more recent version) validate an individual domain name; therefore are not able to validate any wildcard certificates. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">This means that TLS-ALPN-01 is unable to perform any validations for use cases where there will be multiple dynamically generated subdomains (for example, SaaS platforms or multi-tenant applications). The only available option that can be used in these use cases is DNS-01.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Challenges in Multi-server and Load-balanced Environments<\/h3>\n\n\n\n<p class=\"wp-block-paragraph\">In distributed systems where traffic is routed across multiple servers, the TLS-ALPN-01 challenge can be sent to any of the systems. TLS-ALPN-01 adds coordination complexity as it is necessary for each node to be properly configured to answer the challenge. <\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The operational complexity for maintaining consistency of configuration at all nodes creates additional operational risk of failing to validate successfully.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Compare HTTP-01, DNS-01 and TLS-ALPN-01<\/h2>\n\n\n\n<figure class=\"wp-block-table\"><table class=\"has-fixed-layout\"><tbody><tr><td><strong>Feature<\/strong><\/td><td><strong>HTTP-01 Challenge<\/strong><\/td><td><strong>DNS-01 Challenge<\/strong><\/td><td><strong>TLS-ALPN-01 Challenge<\/strong><\/td><\/tr><tr><td><strong>Validation Method<\/strong><\/td><td>Places a token file in the \/.well-known\/acme-challenge\/ directory on a web server<\/td><td>Creates a TXT record in the domain\u2019s DNS configuration<\/td><td>Uses a special self-signed certificate during the TLS handshake with ALPN extension<\/td><\/tr><tr><td><strong>Verification Channel<\/strong><\/td><td>Verified over HTTP via TCP port 80<\/td><td>Verified through DNS record lookup<\/td><td>Verified over TLS via TCP port 443 using ALPN protocol<\/td><\/tr><tr><td><strong>Requires Port 80 Open<\/strong><\/td><td>Yes<\/td><td>No<\/td><td>No<\/td><\/tr><tr><td><strong>Requires Port 443 Open<\/strong><\/td><td>No<\/td><td>No<\/td><td>Yes<\/td><\/tr><tr><td><strong>Requires Web Server Access<\/strong><\/td><td>Yes<\/td><td>No<\/td><td>No (but requires TLS control)<\/td><\/tr><tr><td><strong>Requires DNS Access<\/strong><\/td><td>No<\/td><td>Yes<\/td><td>No<\/td><\/tr><tr><td><strong>Supports Wildcard Certificates<\/strong><\/td><td>No<\/td><td>Yes<\/td><td>No<\/td><\/tr><tr><td><strong>Supports IP Address Validation (ACME DV)<\/strong><\/td><td>No<\/td><td>No<\/td><td>No<\/td><\/tr><tr><td><strong>Automation Difficulty<\/strong><\/td><td>Easy (handled automatically by most ACME clients)<\/td><td>Moderate (requires DNS API or manual TXT updates)<\/td><td>High (requires advanced TLS configuration and support)<\/td><\/tr><tr><td><strong>Validation Speed<\/strong><\/td><td>Fast (usually completes in minutes)<\/td><td>Slower (depends on DNS propagation time)<\/td><td>Fast (similar to HTTP-01 if properly configured)<\/td><\/tr><tr><td><strong>Works Behind CDN<\/strong><\/td><td>Limited (requires correct configuration)<\/td><td>Yes (no routing dependency)<\/td><td>No (breaks with TLS termination)<\/td><\/tr><tr><td><strong>Best For<\/strong><\/td><td>Single-domain websites on standard hosting<\/td><td>Wildcard certificates, cloud, containerized, or restricted environments<\/td><td>Environments with only port 443 open and no DNS automation<\/td><\/tr><tr><td><strong>Common Use Case<\/strong><\/td><td>Public-facing web servers<\/td><td>Multi-subdomain, SaaS, or infrastructure-level deployments<\/td><td>Security-restricted environments or fallback scenarios<\/td><\/tr><tr><td><strong>Implementation Complexity<\/strong><\/td><td>Low<\/td><td>Medium<\/td><td>High<\/td><\/tr><tr><td><strong>Scalability<\/strong><\/td><td>Limited (multi-server coordination needed)<\/td><td>High (centralized via DNS)<\/td><td>Limited (complex in distributed systems)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n<h2 class=\"wp-block-heading\"><a><\/a>Special Considerations for DV Certificates<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">There are some Certificate Authorities (CAs) that require domain validation for each new DV certificate order; there is no validation reuse. Therefore, if you want to automate the issuance or renewals of these types of certificates, you will have to successfully pass the challenge every single time.<\/p>\n\n\n\n<h3 class=\"wp-block-heading\">Additionally:<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>ACME cannot validate IP addresses for DV certificates.<\/li>\n\n\n\n<li>Wildcard domains always require DNS-01.<\/li>\n\n\n\n<li>If your infrastructure restricts port 80, HTTP-01 may fail.<\/li>\n\n\n\n<li>If your DNS provider lacks API support, DNS-01 automation may be difficult.<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">Understanding these operational policies is as important as choosing the challenge type itself.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">When Should You Use HTTP-01?<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Choose HTTP-01 if:<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>You run a standard web server<\/li>\n\n\n\n<li>Port 80 is already open<\/li>\n\n\n\n<li>You are issuing single-domain certificates<\/li>\n\n\n\n<li>You want the simplest automation setup<\/li>\n\n\n\n<li>You don\u2019t need wildcard coverage<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">This is often ideal for small businesses, simple websites, and straightforward hosting environments.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">When Should You Use DNS-01?<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Choose DNS-01 if:<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>You need wildcard certificates<\/li>\n\n\n\n<li>Your infrastructure is cloud-native or containerized<\/li>\n\n\n\n<li>Your server isn\u2019t publicly accessible<\/li>\n\n\n\n<li>Port 80 cannot be opened<\/li>\n\n\n\n<li>You manage multiple subdomains<\/li>\n\n\n\n<li>You require centralized validation control<\/li>\n<\/ul>\n\n\n\n<p class=\"wp-block-paragraph\">DNS-01 is typically better suited for SaaS platforms, enterprise deployments, Kubernetes clusters, and complex hosting setups.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">When Should Use TLS-ALPN-01?<\/h2>\n\n\n\n<h3 class=\"wp-block-heading\">Choose TLS-ALPN-01 if:<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Only HTTPS traffic is permitted<\/li>\n\n\n\n<li>You cannot host the <code>HTTP-01<\/code> challenge<\/li>\n\n\n\n<li>You are using a TLS-terminating proxy<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">So, Which ACME Challenge Is Best?<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">There is no universally \u201cbetter\u201d option,&nbsp; only the one that best fits your infrastructure.<\/p>\n\n\n\n<ul class=\"wp-block-list\">\n<li><strong>For simplicity and speed<\/strong> \u2192 HTTP-01<\/li>\n\n\n\n<li><strong>For flexibility and wildcard support<\/strong> \u2192 DNS-01<\/li>\n\n\n\n<li><strong>For large-scale automation<\/strong> \u2192 DNS-01 with API integration<\/li>\n\n\n\n<li><strong>For basic website deployment<\/strong> \u2192 HTTP-01<\/li>\n<\/ul>\n\n\n\n<h3 class=\"wp-block-heading\">The right choice depends on:<\/h3>\n\n\n\n<ul class=\"wp-block-list\">\n<li>Hosting environment<\/li>\n\n\n\n<li>Security policies<\/li>\n\n\n\n<li>Firewall configuration<\/li>\n\n\n\n<li>DNS automation capabilities<\/li>\n\n\n\n<li>Certificate coverage requirements<\/li>\n<\/ul>\n\n\n\n<h2 class=\"wp-block-heading\">Conclusion<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Regardless of which ACME challenge option you choose, consistent issuance of certificates for your company&#8217;s use of TLS is necessary to ensure your business has consistent TLS security.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">CheapSSLWEB provides you with a simple, affordable, and <a href=\"https:\/\/cheapsslweb.com\/acme\/sectigo-acme-ssl-certificate\">automation-ready SSL Certificate<\/a>. Browse through a large number of DV, OV, EV, and Wildcard Certificates today to ensure the domains of your choice with confidence.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>The validation method selected when issuing SSL\/TLS certificates through the ACME protocol is critical for achieving a seamless automation process and successfully deploying certificates. There are two main challenge types under ACME (HTTP-01 and DNS-01), and while both verify domain control, they do so in very different ways. What are ACME Challenges? ACME challenges are&hellip; <a class=\"more-link\" href=\"https:\/\/cheapsslweb.com\/blog\/acme-challenges-for-domain-validation-which-is-best\/\">Continue reading <span class=\"screen-reader-text\">ACME Challenges for Domain Validation: Which is Best?<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":4308,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[109],"tags":[412,410,411,413],"class_list":["post-4305","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-ssl-certificate","tag-acme-challenge-types","tag-acme-challenges","tag-acme-domain-challenge","tag-http-01-vs-dns-01-vs-tls-alpn-01","entry"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v27.8 - https:\/\/yoast.com\/product\/yoast-seo-wordpress\/ -->\n<title>ACME Challenge Types: HTTP-01 vs DNS-01 vs TLS-ALPN-01 Explained<\/title>\n<meta name=\"description\" content=\"ACME validates control of a domain through a challenge. 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