> ## 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.

# Elixir

> Upsun supports building and deploying applications written in Elixir. There is no default flavor for the build phase, but you can define it explicitly in your build hook. Upsun Elixir images support both committed dependencies and download-on-demand. The underlying Erlang version is 22.0.7.

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 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="elixir" status="supported" platform="grid" />

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

## Deprecated versions

The following versions are still available in your projects,
but they're at their end of life and are no longer receiving security updates from upstream.

<MetaImageVersionList language="elixir" status="deprecated" platform="grid" />

To ensure your project remains stable in the future,
switch to a [supported version](#supported-versions).

## 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="elixir" status="retired" platform="grid" />

### Specify the language

To use Elixir, specify `elixir` 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: 'elixir:<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: 'elixir:{{version:elixir:latest}}'`
  }
</DynamicCodeBlock>

## Built-in variables

Upsun exposes relationships and other configuration as [environment variables](/docs/development/variables).
Most notably, it allows a program to determine at runtime what HTTP port it should listen on
and what the credentials are to access [other services](/docs/add-services).

To get the `PORT` environment variable (the port on which your web application is supposed to listen) you would:

```elixir theme={null}
String.to_integer(System.get_env("PORT") || "8888")
```

Some of the environment variables are in JSON format and are base64 encoded. You would need to import a JSON parsing library such as [JSON](https://hexdocs.pm/json/readme.html) or [Poison](https://hexdocs.pm/poison/api-reference.html) to read those. (There is an example for doing this to decode the `PLATFORM_RELATIONSHIPS` environment variable in the section [below](#accessing-services-manually).)

<Note>
  <h4>Tip</h4>
  Remember `config/prod.exs` is evaluated at **build time** and has no access to runtime configuration. Use `config/releases.exs` to configure your runtime environment.
</Note>

## Building and running the application

If you are using Hex to manage your dependencies, you need to specify the `MIX_ENV` environment variable:

<DynamicCodeBlock language="yaml" filename=".upsun/config.yaml">
  {`
      applications:
        myapp:
          type: 'elixir:{{version:elixir:latest}}'
          variables:
            env:
              MIX_ENV: 'prod'`
  }
</DynamicCodeBlock>

The `SECRET_KEY_BASE` variable is generated automatically based on the [`PLATFORM_PROJECT_ENTROPY` variable](/docs/development/variables/use-variables#use-provided-variables).
You can change it.

Include in your build hook the steps to retrieve a local Hex and `rebar`, and then run `mix do deps.get, deps.compile, compile` on your application to build a binary.

<DynamicCodeBlock language="yaml" filename=".upsun/config.yaml">
  {`
      applications:
        myapp:
          type: 'elixir:{{version:elixir:latest}}'
          hooks:
            build: |
              mix local.hex --force
              mix local.rebar --force
              mix do deps.get --only prod, deps.compile, compile`
  }
</DynamicCodeBlock>

<Note>
  That build hook works for most cases and assumes that your `mix.exs` file is located at [your app root](/docs/configure-apps/app-reference/single-runtime-image#root-directory).
</Note>

Assuming `mix.exs` is present at your app root and your build hook matches the above,
you can then start it from the `web.commands.start` directive.

The following basic app configuration is sufficient to run most Elixir applications.

<DynamicCodeBlock language="yaml" filename=".upsun/config.yaml">
  {`
      applications:
        myapp:
          type: 'elixir:{{version:elixir:latest}}'

          variables:
            env:
              MIX_ENV: 'prod'

          hooks:
            build: |
              mix local.hex --force
              mix local.rebar --force
              mix do deps.get --only prod, deps.compile, compile

          web:
            commands:
              start: mix phx.server
            locations:
              /:
                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 Elixir application unconditionally, as in the example above.

## Dependencies

The recommended way to handle Elixir dependencies on Upsun is using Hex.
You can commit a `mix.exs` file in your repository and the system downloads the dependencies in your `deps` section using the build hook above.

```elixir theme={null}
  defp deps do
    [
	  {:platformshconfig, "~> 0.1.0"}
    ]
  end
```

## Accessing Services

<MetaServiceList />

### Accessing Services Manually

The services configuration is available in the environment variable `PLATFORM_RELATIONSHIPS`.

Given a [relationship](/docs/configure-apps/image-properties/relationships) defined in `.upsun/config.yaml`:

<DynamicCodeBlock language="yaml" filename=".upsun/config.yaml">
  {`
      applications:
        myapp:
          type: 'elixir:{{version:elixir:latest}}'

          [...]

          # Relationships enable an app container's access to a service.
          # The example below shows simplified configuration leveraging a default service
          # (identified from the relationship name) and a default endpoint.
          # See the Application reference for all options for defining relationships and endpoints.
          relationships:
            postgresql:`
  }
</DynamicCodeBlock>

Assuming you have in `mix.exs` the Poison library to parse JSON:

```elixir theme={null}
  defp deps do
    [
      {:poison, "~> 3.0"}
    ]
  end
```

And assuming you use `ecto` you could put in `config/config.exs`:

```elixir theme={null}
relationships = Poison.decode!(Base.decode64!(System.get_env("PLATFORM_RELATIONSHIPS")))
[postgresql_config | _tail] = relationships["postgresql"]

config :my_app, Repo,
  database: postgresql_config["path"],
  username: postgresql_config["username"],
  password: postgresql_config["password"],
  hostname: postgresql_config["host"]
```

and setup Ecto during the deploy hook:

```yaml .upsun/config.yaml theme={null}
applications:
  myapp:
    hooks:
      deploy: |
        mix do ecto.setup
```

## View application instance details

To understand how an application's instances are distributed, you can view the instance details in the project's `/run/peers.json` file. To learn more, see [View application instance details](/docs/manage-resources/adjust-resources#view-application-instance-details) in the "Resource configuration" topic.