> ## Documentation Index
> Fetch the complete documentation index at: https://developer.upsun.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Go

> Upsun supports building and deploying applications written in Go using Go modules. They're compiled during the Build hook phase, and support both committed dependencies and download-on-demand.

export const DynamicCodeBlock = ({language = 'yaml', filename, icon, lines, wrap, expandable, highlight, focus, children}) => {
  const STORAGE_KEY = 'upsun_versions_cache';
  const COMPOSABLE_STORAGE_KEY = 'upsun_composable_cache';
  const CACHE_TTL = 5 * 60 * 1000;
  const API_URL = 'https://meta.upsun.com/images';
  const COMPOSABLE_API_URL = 'https://meta.upsun.com/composable';
  const DEBUG_PREFIX = '[DynamicCodeBlock cache]';
  const [versionData, setVersionData] = useState(null);
  const [versionError, setVersionError] = useState(false);
  const [composableData, setComposableData] = useState(null);
  const [composableError, setComposableError] = useState(false);
  useEffect(() => {
    const fetchData = async () => {
      let cachedData = null;
      let cachedEtag = null;
      if (typeof localStorage !== 'undefined') {
        try {
          const cached = localStorage.getItem(STORAGE_KEY);
          if (cached) {
            const parsed = JSON.parse(cached);
            cachedData = parsed?.data || null;
            cachedEtag = parsed?.etag || null;
            if (cachedData && Date.now() - parsed.timestamp < CACHE_TTL) {
              return cachedData;
            }
          }
        } catch (err) {
          console.error('Failed to load from cache:', err);
        }
      }
      const requestHeaders = cachedEtag ? {
        'If-None-Match': cachedEtag
      } : {};
      console.debug(`${DEBUG_PREFIX} revalidating`, {
        storageKey: STORAGE_KEY,
        hasCachedData: Boolean(cachedData),
        hasCachedEtag: Boolean(cachedEtag)
      });
      const response = await fetch(API_URL, {
        headers: requestHeaders
      });
      if (response.status === 304 && cachedData) {
        console.debug(`${DEBUG_PREFIX} revalidated (304)`, {
          storageKey: STORAGE_KEY
        });
        if (typeof localStorage !== 'undefined') {
          try {
            const etag = response.headers.get('etag') || cachedEtag;
            localStorage.setItem(STORAGE_KEY, JSON.stringify({
              data: cachedData,
              etag,
              timestamp: Date.now()
            }));
          } catch (err) {
            console.error('Failed to refresh cache metadata:', err);
          }
        }
        return cachedData;
      }
      if (!response.ok) throw new Error(`API request failed: ${response.statusText}`);
      const data = await response.json();
      const etag = response.headers.get('etag');
      console.debug(`${DEBUG_PREFIX} refreshed (200)`, {
        storageKey: STORAGE_KEY,
        etag
      });
      if (typeof localStorage !== 'undefined') {
        try {
          localStorage.setItem(STORAGE_KEY, JSON.stringify({
            data,
            etag,
            timestamp: Date.now()
          }));
        } catch (err) {
          console.error('Failed to cache data:', err);
        }
      }
      return data;
    };
    fetchData().then(data => setVersionData(data)).catch(err => console.error('Failed to fetch version data:', err));
  }, []);
  const findHighestVersion = versionsMap => {
    if (!versionsMap || Object.keys(versionsMap).length === 0) return null;
    const entries = Object.entries(versionsMap);
    const active = entries.filter(([, v]) => v.upsun && v.upsun.status === 'supported' || v.upsun && v.upsun.status === 'deprecated');
    const candidates = active.length > 0 ? active : entries;
    let [highestName] = candidates[0];
    for (let i = 1; i < candidates.length; i++) {
      const [currentName] = candidates[i];
      const cp = currentName.split('.').map(Number);
      const hp = highestName.split('.').map(Number);
      for (let j = 0; j < Math.max(cp.length, hp.length); j++) {
        if ((cp[j] || 0) > (hp[j] || 0)) {
          highestName = currentName;
          break;
        } else if ((cp[j] || 0) < (hp[j] || 0)) {
          break;
        }
      }
    }
    return highestName;
  };
  const getVersion = (lang, requestedVersion = 'latest') => {
    if (lang === 'composable') {
      if (!composableData || !composableData.versions || Object.keys(composableData.versions).length === 0) return null;
      if (requestedVersion && requestedVersion !== 'latest') {
        return (requestedVersion in composableData.versions) ? requestedVersion : null;
      }
      return findHighestVersion(composableData.versions);
    }
    if (!versionData) return null;
    const imageData = versionData[lang];
    if (!imageData || !imageData.versions || Object.keys(imageData.versions).length === 0) {
      return null;
    }
    if (requestedVersion && requestedVersion !== 'latest') {
      return (requestedVersion in imageData.versions) ? requestedVersion : null;
    }
    return findHighestVersion(imageData.versions);
  };
  let code = typeof children === 'string' ? children : String(children || '');
  const codeLines = code.split('\n');
  while (codeLines.length > 0 && codeLines[0].trim() === '') codeLines.shift();
  while (codeLines.length > 0 && codeLines[codeLines.length - 1].trim() === '') codeLines.pop();
  if (codeLines.length > 0) {
    const indents = codeLines.filter(line => line.trim().length > 0).map(line => line.match(/^[ \t]*/)[0].length);
    const minIndent = Math.min(...indents);
    code = codeLines.map(line => line.slice(minIndent)).join('\n');
  }
  code = code.replace(/\{\{version:(.*?)\}\}/g, (match, params) => {
    const parts = params.split(':');
    const lang = parts[0];
    const ver = parts[1] || 'latest';
    const isComposable = lang === 'composable';
    const hasError = isComposable ? composableError : versionError;
    const dataReady = isComposable ? composableData !== null : versionData !== null;
    if (hasError) return '(unavailable)';
    if (dataReady) {
      const resolvedVersion = getVersion(lang, ver);
      return resolvedVersion || match;
    }
    return '...';
  });
  const codeBlockProps = {
    language,
    ...filename && ({
      filename
    }),
    ...icon && ({
      icon
    }),
    ...lines !== undefined && ({
      lines
    }),
    ...wrap !== undefined && ({
      wrap
    }),
    ...expandable !== undefined && ({
      expandable
    }),
    ...highlight && ({
      highlight
    }),
    ...focus && ({
      focus
    })
  };
  return <CodeBlock {...codeBlockProps}>{code}</CodeBlock>;
};

export const RepoList = ({lang, displayName}) => <Info>
    To deploy a {displayName} project, create a new project from the{' '}
    <a href="https://console.upsun.com/projects/create-project">Upsun Console</a>{' '}
    and select a template, or push your existing code.
  </Info>;

export const VersionDeprecatedBlock = () => <>
    <h3 id="deprecated-versions">Deprecated versions</h3>
    <p>
    The following versions are <a href="/docs/glossary#deprecated-versions">deprecated</a>.
    They're available, but they don't receive security updates from upstream and aren't guaranteed to work.
    They'll be removed in the future – consider migrating to a <a href="#supported-versions">supported version</a>.
    </p>
  </>;

export const MetaServiceList = () => {
  const [services, setServices] = useState([]);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);
  const STORAGE_KEY = 'upsun_versions_internal_cache';
  const CACHE_TTL = 1 * 60 * 60 * 1000;
  const API_URL = 'https://meta.upsun.com/images';
  const findHighestVersion = versionsMap => {
    if (!versionsMap || Object.keys(versionsMap).length === 0) return null;
    const entries = Object.entries(versionsMap);
    const active = entries.filter(([, v]) => v.upsun && v.upsun.status === 'supported' || v.upsun && v.upsun.status === 'deprecated');
    const candidates = active.length > 0 ? active : entries;
    let [highestName] = candidates[0];
    for (let i = 1; i < candidates.length; i++) {
      const [currentName] = candidates[i];
      const cp = currentName.split('.').map(Number);
      const hp = highestName.split('.').map(Number);
      for (let j = 0; j < Math.max(cp.length, hp.length); j++) {
        if ((cp[j] || 0) > (hp[j] || 0)) {
          highestName = currentName;
          break;
        } else if ((cp[j] || 0) < (hp[j] || 0)) {
          break;
        }
      }
    }
    return highestName;
  };
  useEffect(() => {
    setLoading(true);
    setError(null);
    const fetchData = async () => {
      let cachedData = null;
      let cachedEtag = null;
      if (typeof localStorage !== 'undefined') {
        try {
          const cached = localStorage.getItem(STORAGE_KEY);
          if (cached) {
            const parsed = JSON.parse(cached);
            cachedData = parsed?.data || null;
            cachedEtag = parsed?.etag || null;
            if (cachedData && Date.now() - parsed.timestamp < CACHE_TTL) return cachedData;
          }
        } catch (error_) {
          console.error('Failed to load from cache:', error_);
        }
      }
      const requestHeaders = {
        ...cachedEtag && ({
          'If-None-Match': cachedEtag
        }),
        internal: 'true'
      };
      const response = await fetch(API_URL, {
        headers: requestHeaders
      });
      if (response.status === 304 && cachedData) {
        if (typeof localStorage !== 'undefined') {
          try {
            const etag = response.headers.get('etag') || cachedEtag;
            localStorage.setItem(STORAGE_KEY, JSON.stringify({
              data: cachedData,
              etag,
              timestamp: Date.now()
            }));
          } catch (error_) {
            console.error('Failed to refresh cache metadata:', error_);
          }
        }
        return cachedData;
      }
      if (!response.ok) throw new Error(`API request failed: ${response.statusText}`);
      const data = await response.json();
      const etag = response.headers.get('etag');
      if (typeof localStorage !== 'undefined') {
        try {
          localStorage.setItem(STORAGE_KEY, JSON.stringify({
            data,
            etag,
            timestamp: Date.now()
          }));
        } catch (error_) {
          console.error('Failed to cache data:', error_);
        }
      }
      return data;
    };
    fetchData().then(data => {
      if (!data) {
        setServices([]);
        setLoading(false);
        return;
      }
      const serviceList = [];
      for (const [serviceType, imageData] of Object.entries(data)) {
        if (imageData.service && imageData.versions && Object.keys(imageData.versions).length > 0) {
          const highest = findHighestVersion(imageData.versions);
          let serviceUrl = imageData.docs.url;
          switch (serviceType) {
            case 'mariadb':
            case 'mariadb-replica':
            case 'postgresql-replica':
            case 'oracle-mysql':
            case 'mongodb-enterprise':
            case 'elasticsearch-enterprise':
              {
                continue;
              }
            default:
              {
                serviceUrl = `${serviceUrl}#usage-example`;
                break;
              }
          }
          serviceList.push({
            type: serviceType,
            name: imageData.name || serviceType,
            version: highest || 'N/A',
            url: `${serviceUrl}`
          });
        }
      }
      serviceList.sort((a, b) => a.name.localeCompare(b.name));
      setServices(serviceList);
      setLoading(false);
    }).catch(error_ => {
      console.error('MetaServiceList error:', error_);
      setError(error_.message);
      setLoading(false);
    });
  }, []);
  if (loading) return <p>Loading services...</p>;
  if (error) return <p>Error: {error}</p>;
  if (!services || services.length === 0) return <p>No services found.</p>;
  return <>
      <p>
        You can access service credentials to connect to{' '}
        <a href="/docs/add-services">managed services</a>{' '}
        from environment variables present in the application container.
        Consult each of the individual service documentation to see how to retrieve and surface credentials into your application.
      </p>
      <ul>
        {services.map(service => <li key={service.name}>
            <a href={service.url} target="_self">{service.name}</a>
          </li>)}
        <li key="Chroma">
          <a href="/tutorials/self-hosted/chroma#3-use-the-relationship-in-your-application">Chroma</a>
        </li>
        <li key="Qdrant">
          <a href="/tutorials/self-hosted/qdrant#4-use-the-relationship-in-your-application">Qdrant</a>
        </li>
      </ul>
    </>;
};

export const MetaImageVersionList = ({language, status}) => {
  const [versions, setVersions] = useState([]);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);
  const STORAGE_KEY = 'upsun_versions_cache';
  const CACHE_TTL = 5 * 60 * 1000;
  const API_URL = 'https://meta.upsun.com/images';
  useEffect(() => {
    if (!language) {
      setLoading(false);
      return;
    }
    setLoading(true);
    setError(null);
    const fetchData = async () => {
      let cachedData = null;
      let cachedEtag = null;
      if (typeof localStorage !== 'undefined') {
        try {
          const cached = localStorage.getItem(STORAGE_KEY);
          if (cached) {
            const parsed = JSON.parse(cached);
            cachedData = parsed?.data || null;
            cachedEtag = parsed?.etag || null;
            if (cachedData && Date.now() - parsed.timestamp < CACHE_TTL) return cachedData;
          }
        } catch (error_) {
          console.error('Failed to load from cache:', error_);
        }
      }
      const requestHeaders = cachedEtag ? {
        'If-None-Match': cachedEtag
      } : {};
      const response = await fetch(API_URL, {
        headers: requestHeaders
      });
      if (response.status === 304 && cachedData) {
        if (typeof localStorage !== 'undefined') {
          try {
            const etag = response.headers.get('etag') || cachedEtag;
            localStorage.setItem(STORAGE_KEY, JSON.stringify({
              data: cachedData,
              etag,
              timestamp: Date.now()
            }));
          } catch (error_) {
            console.error('Failed to refresh cache metadata:', error_);
          }
        }
        return cachedData;
      }
      if (!response.ok) throw new Error(`API request failed: ${response.statusText}`);
      const data = await response.json();
      const etag = response.headers.get('etag');
      if (typeof localStorage !== 'undefined') {
        try {
          localStorage.setItem(STORAGE_KEY, JSON.stringify({
            data,
            etag,
            timestamp: Date.now()
          }));
        } catch (error_) {
          console.error('Failed to cache data:', error_);
        }
      }
      return data;
    };
    fetchData().then(data => {
      if (!data || !data[language]) {
        setVersions([]);
        setLoading(false);
        return;
      }
      const imageData = data[language];
      if (!imageData.versions) {
        setVersions([]);
        setLoading(false);
        return;
      }
      let versionList = Object.entries(imageData.versions).map(([name, v]) => ({
        name,
        status: v.upsun?.status || v.status
      })).sort((a, b) => {
        const aParts = a.name.split('.').map(Number);
        const bParts = b.name.split('.').map(Number);
        const max = Math.max(aParts.length, bParts.length);
        for (let i = 0; i < max; i++) {
          const av = aParts[i] || 0;
          const bv = bParts[i] || 0;
          if (av !== bv) return bv - av;
        }
        return 0;
      });
      if (status) {
        versionList = versionList.filter(v => v.status === status);
      }
      setVersions(versionList);
      setLoading(false);
    }).catch(error_ => {
      console.error('MetaImageVersionList error:', error_);
      setError(error_.message);
      setLoading(false);
    });
  }, [language, status]);
  if (loading) return <p>Loading...</p>;
  if (error) return <p>Error: {error}</p>;
  if (!versions || versions.length === 0) {
    if (status === 'incoming') return null;
    return <p>No versions available! Contact support.</p>;
  }
  let incomingBlock = null;
  if (status === 'incoming' && versions.length > 0) {
    incomingBlock = `These versions are not yet available but are expected to be released soon.`;
  }
  return incomingBlock ? <Note>
      <p>{incomingBlock}</p>
      <ul>
        {versions.map(version => <li className="image-version" key={version.name}>
            {version.name} {version.status === 'beta' && <span className="badge">Beta</span>}
          </li>)}
      </ul>
    </Note> : <ul>
      {versions.map(version => <li className="image-version" key={version.name}>
          {version.name} {version.status === 'beta' && <span className="badge">Beta</span>}
        </li>)}
    </ul>;
};

export const MetaImageVersion = ({language, version}) => {
  const [selectedVersion, setSelectedVersion] = useState(null);
  const [loading, setLoading] = useState(true);
  const [error, setError] = useState(null);
  const isComposable = language === 'composable';
  const STORAGE_KEY = isComposable ? 'upsun_composable_cache' : 'upsun_versions_cache';
  const CACHE_TTL = 5 * 60 * 1000;
  const API_URL = isComposable ? 'https://meta.upsun.com/composable' : 'https://meta.upsun.com/images';
  const findHighestVersion = versionsMap => {
    if (!versionsMap || Object.keys(versionsMap).length === 0) return null;
    const entries = Object.entries(versionsMap);
    const active = entries.filter(([, v]) => v.upsun && v.upsun.status === 'supported' || v.upsun && v.upsun.status === 'deprecated');
    const candidates = active.length > 0 ? active : entries;
    let [highestName] = candidates[0];
    for (let i = 1; i < candidates.length; i++) {
      const [currentName] = candidates[i];
      const cp = currentName.split('.').map(Number);
      const hp = highestName.split('.').map(Number);
      for (let j = 0; j < Math.max(cp.length, hp.length); j++) {
        if ((cp[j] || 0) > (hp[j] || 0)) {
          highestName = currentName;
          break;
        } else if ((cp[j] || 0) < (hp[j] || 0)) {
          break;
        }
      }
    }
    return highestName;
  };
  useEffect(() => {
    if (!language) {
      setLoading(false);
      return;
    }
    setLoading(true);
    setError(null);
    const fetchData = async () => {
      let cachedData = null;
      let cachedEtag = null;
      if (typeof localStorage !== 'undefined') {
        try {
          const cached = localStorage.getItem(STORAGE_KEY);
          if (cached) {
            const parsed = JSON.parse(cached);
            cachedData = parsed?.data || null;
            cachedEtag = parsed?.etag || null;
            if (cachedData && Date.now() - parsed.timestamp < CACHE_TTL) return cachedData;
          }
        } catch (error_) {
          console.error('Failed to load from cache:', error_);
        }
      }
      const requestHeaders = cachedEtag ? {
        'If-None-Match': cachedEtag
      } : {};
      const response = await fetch(API_URL, {
        headers: requestHeaders
      });
      if (response.status === 304 && cachedData) {
        if (typeof localStorage !== 'undefined') {
          try {
            const etag = response.headers.get('etag') || cachedEtag;
            localStorage.setItem(STORAGE_KEY, JSON.stringify({
              data: cachedData,
              etag,
              timestamp: Date.now()
            }));
          } catch (error_) {
            console.error('Failed to refresh cache metadata:', error_);
          }
        }
        return cachedData;
      }
      if (!response.ok) throw new Error(`API request failed: ${response.statusText}`);
      const data = await response.json();
      const etag = response.headers.get('etag');
      if (typeof localStorage !== 'undefined') {
        try {
          localStorage.setItem(STORAGE_KEY, JSON.stringify({
            data,
            etag,
            timestamp: Date.now()
          }));
        } catch (error_) {
          console.error('Failed to cache data:', error_);
        }
      }
      return data;
    };
    fetchData().then(data => {
      if (!data) {
        setSelectedVersion(null);
        setLoading(false);
        return;
      }
      const imageData = isComposable ? data : data[language];
      if (!imageData || !imageData.versions || Object.keys(imageData.versions).length === 0) {
        setSelectedVersion(null);
        setLoading(false);
        return;
      }
      let versionName = null;
      if (version && version !== 'latest') {
        versionName = (version in imageData.versions) ? version : null;
      } else {
        versionName = findHighestVersion(imageData.versions);
      }
      setSelectedVersion(versionName);
      setLoading(false);
    }).catch(error_ => {
      console.error('MetaImageVersion error:', error_);
      setError(error_.message);
      setLoading(false);
    });
  }, [language, version]);
  if (loading) return <span>…</span>;
  if (error) return <span title={error}>⚠ unavailable</span>;
  if (!selectedVersion) return <span>No version found</span>;
  return <span>{selectedVersion}</span>;
};

export const DisclaimerNix = () => <Tip>
    You can now use composable image to install runtimes and tools in your application container. To find out more, see the <a href="/docs/configure-apps/app-reference/composable-image">Composable image</a> topic.
  </Tip>;

<DisclaimerNix />

## Supported versions

You can select the major and minor version.

Patch versions are applied periodically for bug fixes and the like.
When you deploy your app, you always get the latest available patches.

<MetaImageVersionList language="golang" status="supported" platform="grid" />

<MetaImageVersionList language="golang" status="incoming" platform="grid" />

### Specify the language

To use Go, specify `golang` as your [app's `type`](/docs/configure-apps/app-reference/single-runtime-image#type):

<DynamicCodeBlock language="yaml" filename=".upsun/config.yaml">
  {`
      applications:
        # The app's name, which must be unique within the project.
        <APP_NAME>:
          type: 'golang:<VERSION_NUMBER>'
    `
  }
</DynamicCodeBlock>

For example:

<DynamicCodeBlock language="yaml" filename=".upsun/config.yaml">
  {`
      applications:
        # The app's name, which must be unique within the project.
        myapp:
          type: 'golang:{{version:golang:latest}}'`
  }
</DynamicCodeBlock>

<VersionDeprecatedBlock />

<MetaImageVersionList language="golang" status="deprecated" />

## Retired versions

The following versions have been retired and are no longer available.
If your project uses a retired version, you must update to a [supported version](#supported-versions).

<MetaImageVersionList language="golang" status="retired" />

## Go toolchain auto download

Even though you select a specific version of Go, starting in Go 1.21, the `go` command will automatically download and use a different toolchain version as requested by the `toolchain` directive in `go.mod`, or the `GOTOOLCHAIN` environmental variable (see [Go Toolchains](https://go.dev/doc/toolchain)).

<Note>
  Still, it is important to keep your chosen version of Go updated in your yaml configuration file. This will ensure that you are using the most up to date software for your projects.
</Note>

## Go modules

The recommended way to handle Go dependencies on Upsun is using Go module support in Go 1.11 and later. That allows the build process to use `go build` directly without any extra steps, and you can specify an output executable file of your choice. (See the examples below.)

## Building and running the application

Assuming your `go.mod` and `go.sum` files are present in your repository, your application can be built with the command `go build`, to produce a working executable. You can then start it from the `web.commands.start` directive. Note that the start command *must* run in the foreground. If the program terminates for any reason it is automatically restarted.

The following basic `.upsun/config.yaml` file is sufficient to run most Go applications.

<DynamicCodeBlock language="yaml" filename=".upsun/config.yaml">
  {`
      applications:
        # The app's name, which must be unique within the project.
        myapp:
          type: 'golang:{{version:golang:latest}}'

          hooks:
            build: |
              # Modify this line if you want to build differently or
              # use an alternate name for your executable.
              go build -o bin/app

          web:
            upstream:
              socket_family: tcp
              protocol: http

            commands:
              # If you change the build output in the build hook above, update this line as well.
              start: ./bin/app

            locations:
              /:
                # Route all requests to the Go app, unconditionally.
                allow: false
                passthru: true`
  }
</DynamicCodeBlock>

Note that there is still an Nginx proxy server sitting in front of your application.
If desired, certain paths may be served directly by Nginx without hitting your application (for static files, primarily)
or you may route all requests to the Go application unconditionally, as in the example above.

## Accessing services

To access various [services](/docs/add-services) with Go, see the following examples. The individual service pages have more information on configuring each service.

<MetaServiceList />

<RepoList lang="golang" displayName="Go" />