feat: Auto select workspace proxy based on lowest latency (#7515)

* feat: Proxy auto select and user selection state
* chore: Auto select based on latency
* Add extra test for unknown latencies
* Mock latencies for unit tests

site/jest.setup.ts

@@ -8,6 +8,7 @@ import { Blob } from "buffer"
 import jestFetchMock from "jest-fetch-mock"
 import { ProxyLatencyReport } from "contexts/useProxyLatency"
 import { RegionsResponse } from "api/typesGenerated"
+import { useMemo } from "react"
 
 jestFetchMock.enableMocks()
 
@@ -16,20 +17,25 @@ jestFetchMock.enableMocks()
 // actual network requests. So just globally mock this hook.
 jest.mock("contexts/useProxyLatency", () => ({
   useProxyLatency: (proxies?: RegionsResponse) => {
-    if (!proxies) {
-      return {} as Record<string, ProxyLatencyReport>
-    }
-
-    return proxies.regions.reduce((acc, proxy) => {
-      acc[proxy.id] = {
-        accurate: true,
-        // Return a constant latency of 8ms.
-        // If you make this random it could break stories.
-        latencyMS: 8,
-        at: new Date(),
+    // Must use `useMemo` here to avoid infinite loop.
+    // Mocking the hook with a hook.
+    const latencies = useMemo(() => {
+      if (!proxies) {
+        return {} as Record<string, ProxyLatencyReport>
       }
-      return acc
-    }, {} as Record<string, ProxyLatencyReport>)
+      return proxies.regions.reduce((acc, proxy) => {
+        acc[proxy.id] = {
+          accurate: true,
+          // Return a constant latency of 8ms.
+          // If you make this random it could break stories.
+          latencyMS: 8,
+          at: new Date(),
+        }
+        return acc
+      }, {} as Record<string, ProxyLatencyReport>)
+    }, [proxies])
+
+    return latencies
   },
 }))
 

site/src/components/AppLink/AppLink.stories.tsx

@@ -26,6 +26,9 @@ const Template: Story<AppLinkProps> = (args) => (
       setProxy: () => {
         return
       },
+      clearProxy: () => {
+        return
+      },
     }}
   >
     <AppLink {...args} />

site/src/components/Resources/AgentRow.stories.tsx

@@ -65,6 +65,9 @@ const TemplateFC = (
         setProxy: () => {
           return
         },
+        clearProxy: () => {
+          return
+        },
       }}
     >
       <AgentRow {...args} />

site/src/components/Resources/ResourceCard.stories.tsx

@@ -30,6 +30,9 @@ Example.args = {
         setProxy: () => {
           return
         },
+        clearProxy: () => {
+          return
+        },
       }}
     >
       <AgentRow
@@ -97,6 +100,9 @@ BunchOfMetadata.args = {
         setProxy: () => {
           return
         },
+        clearProxy: () => {
+          return
+        },
       }}
     >
       <AgentRow

site/src/components/Workspace/Workspace.stories.tsx

@@ -47,6 +47,9 @@ const Template: Story<WorkspaceProps> = (args) => (
         proxies: [],
         isLoading: false,
         isFetched: true,
+        clearProxy: () => {
+          return
+        },
         setProxy: () => {
           return
         },

site/src/contexts/ProxyContext.test.ts

@@ -1,62 +0,0 @@
-import {
-  MockPrimaryWorkspaceProxy,
-  MockWorkspaceProxies,
-  MockHealthyWildWorkspaceProxy,
-  MockUnhealthyWildWorkspaceProxy,
-} from "testHelpers/entities"
-import { getPreferredProxy } from "./ProxyContext"
-
-describe("ProxyContextGetURLs", () => {
-  it.each([
-    ["empty", [], undefined, "", ""],
-    // Primary has no path app URL. Uses relative links
-    [
-      "primary",
-      [MockPrimaryWorkspaceProxy],
-      MockPrimaryWorkspaceProxy,
-      "",
-      MockPrimaryWorkspaceProxy.wildcard_hostname,
-    ],
-    [
-      "regions selected",
-      MockWorkspaceProxies,
-      MockHealthyWildWorkspaceProxy,
-      MockHealthyWildWorkspaceProxy.path_app_url,
-      MockHealthyWildWorkspaceProxy.wildcard_hostname,
-    ],
-    // Primary is the default if none selected
-    [
-      "no selected",
-      [MockPrimaryWorkspaceProxy],
-      undefined,
-      "",
-      MockPrimaryWorkspaceProxy.wildcard_hostname,
-    ],
-    [
-      "regions no select primary default",
-      MockWorkspaceProxies,
-      undefined,
-      "",
-      MockPrimaryWorkspaceProxy.wildcard_hostname,
-    ],
-    // Primary is the default if the selected is unhealthy
-    [
-      "unhealthy selection",
-      MockWorkspaceProxies,
-      MockUnhealthyWildWorkspaceProxy,
-      "",
-      MockPrimaryWorkspaceProxy.wildcard_hostname,
-    ],
-    // This should never happen, when there is no primary
-    ["no primary", [MockHealthyWildWorkspaceProxy], undefined, "", ""],
-  ])(
-    `%p`,
-    (_, regions, selected, preferredPathAppURL, preferredWildcardHostname) => {
-      const preferred = getPreferredProxy(regions, selected)
-      expect(preferred.preferredPathAppURL).toBe(preferredPathAppURL)
-      expect(preferred.preferredWildcardHostname).toBe(
-        preferredWildcardHostname,
-      )
-    },
-  )
-})

site/src/contexts/ProxyContext.test.tsx

@@ -0,0 +1,386 @@
+import {
+  MockPrimaryWorkspaceProxy,
+  MockWorkspaceProxies,
+  MockHealthyWildWorkspaceProxy,
+  MockUnhealthyWildWorkspaceProxy,
+} from "testHelpers/entities"
+import {
+  getPreferredProxy,
+  ProxyProvider,
+  saveUserSelectedProxy,
+  useProxy,
+} from "./ProxyContext"
+import * as ProxyLatency from "./useProxyLatency"
+import {
+  renderWithAuth,
+  waitForLoaderToBeRemoved,
+} from "testHelpers/renderHelpers"
+import { screen } from "@testing-library/react"
+import { server } from "testHelpers/server"
+import { rest } from "msw"
+import { Region } from "api/typesGenerated"
+import "testHelpers/localstorage"
+import userEvent from "@testing-library/user-event"
+
+// Mock useProxyLatency to use a hard-coded latency. 'jest.mock' must be called
+// here and not inside a unit test.
+jest.mock("contexts/useProxyLatency", () => ({
+  useProxyLatency: () => {
+    return hardCodedLatencies
+  },
+}))
+
+let hardCodedLatencies: Record<string, ProxyLatency.ProxyLatencyReport> = {}
+
+// fakeLatency is a helper function to make a Latency report from just a number.
+const fakeLatency = (ms: number): ProxyLatency.ProxyLatencyReport => {
+  return {
+    latencyMS: ms,
+    accurate: true,
+    at: new Date(),
+  }
+}
+
+describe("ProxyContextGetURLs", () => {
+  it.each([
+    ["empty", [], {}, undefined, "", ""],
+    // Primary has no path app URL. Uses relative links
+    [
+      "primary",
+      [MockPrimaryWorkspaceProxy],
+      {},
+      MockPrimaryWorkspaceProxy,
+      "",
+      MockPrimaryWorkspaceProxy.wildcard_hostname,
+    ],
+    [
+      "regions selected",
+      MockWorkspaceProxies,
+      {},
+      MockHealthyWildWorkspaceProxy,
+      MockHealthyWildWorkspaceProxy.path_app_url,
+      MockHealthyWildWorkspaceProxy.wildcard_hostname,
+    ],
+    // Primary is the default if none selected
+    [
+      "no selected",
+      [MockPrimaryWorkspaceProxy],
+      {},
+      undefined,
+      "",
+      MockPrimaryWorkspaceProxy.wildcard_hostname,
+    ],
+    [
+      "regions no select primary default",
+      MockWorkspaceProxies,
+      {},
+      undefined,
+      "",
+      MockPrimaryWorkspaceProxy.wildcard_hostname,
+    ],
+    // Primary is the default if the selected is unhealthy
+    [
+      "unhealthy selection",
+      MockWorkspaceProxies,
+      {},
+      MockUnhealthyWildWorkspaceProxy,
+      "",
+      MockPrimaryWorkspaceProxy.wildcard_hostname,
+    ],
+    // This should never happen, when there is no primary
+    ["no primary", [MockHealthyWildWorkspaceProxy], {}, undefined, "", ""],
+    // Latency behavior
+    [
+      "best latency",
+      MockWorkspaceProxies,
+      {
+        [MockPrimaryWorkspaceProxy.id]: fakeLatency(100),
+        [MockHealthyWildWorkspaceProxy.id]: fakeLatency(50),
+        // This should be ignored because it's unhealthy
+        [MockUnhealthyWildWorkspaceProxy.id]: fakeLatency(25),
+        // This should be ignored because it is not in the list.
+        ["not a proxy"]: fakeLatency(10),
+      },
+      undefined,
+      MockHealthyWildWorkspaceProxy.path_app_url,
+      MockHealthyWildWorkspaceProxy.wildcard_hostname,
+    ],
+  ])(
+    `%p`,
+    (
+      _,
+      regions,
+      latencies,
+      selected,
+      preferredPathAppURL,
+      preferredWildcardHostname,
+    ) => {
+      const preferred = getPreferredProxy(regions, selected, latencies)
+      expect(preferred.preferredPathAppURL).toBe(preferredPathAppURL)
+      expect(preferred.preferredWildcardHostname).toBe(
+        preferredWildcardHostname,
+      )
+    },
+  )
+})
+
+const TestingComponent = () => {
+  return renderWithAuth(
+    <ProxyProvider>
+      <TestingScreen />
+    </ProxyProvider>,
+    {
+      route: `/proxies`,
+      path: "/proxies",
+    },
+  )
+}
+
+// TestingScreen just mounts some components that we can check in the unit test.
+const TestingScreen = () => {
+  const { proxy, userProxy, isFetched, isLoading, clearProxy, setProxy } =
+    useProxy()
+  return (
+    <>
+      <div data-testid="isFetched" title={isFetched.toString()}></div>
+      <div data-testid="isLoading" title={isLoading.toString()}></div>
+      <div
+        data-testid="preferredProxy"
+        title={proxy.proxy && proxy.proxy.id}
+      ></div>
+      <div data-testid="userProxy" title={userProxy && userProxy.id}></div>
+      <button data-testid="clearProxy" onClick={clearProxy}></button>
+      <div data-testid="userSelectProxyData"></div>
+      <button
+        data-testid="userSelectProxy"
+        onClick={() => {
+          const data = screen.getByTestId("userSelectProxyData")
+          if (data.innerText) {
+            setProxy(JSON.parse(data.innerText))
+          }
+        }}
+      ></button>
+    </>
+  )
+}
+
+interface ProxyContextSelectionTest {
+  // Regions is the list of regions to return via the "api" response.
+  regions: Region[]
+  // storageProxy should be the proxy stored in local storage before the
+  // component is mounted and context is loaded. This simulates opening a
+  // new window with a selection saved from before.
+  storageProxy: Region | undefined
+  // latencies is the hard coded latencies to return. If empty, no latencies
+  // are returned.
+  latencies?: Record<string, ProxyLatency.ProxyLatencyReport>
+  // afterLoad are actions to take after loading the component, but before
+  // assertions. This is useful for simulating user actions.
+  afterLoad?: () => Promise<void>
+
+  // Assert these values.
+  // expProxyID is the proxyID returned to be used.
+  expProxyID: string
+  // expUserProxyID is the user's stored selection.
+  expUserProxyID?: string
+}
+
+describe("ProxyContextSelection", () => {
+  beforeEach(() => {
+    window.localStorage.clear()
+  })
+
+  // A way to simulate a user clearing the proxy selection.
+  const clearProxyAction = async (): Promise<void> => {
+    const user = userEvent.setup()
+    const clearProxyButton = screen.getByTestId("clearProxy")
+    await user.click(clearProxyButton)
+  }
+
+  const userSelectProxy = (proxy: Region): (() => Promise<void>) => {
+    return async (): Promise<void> => {
+      const user = userEvent.setup()
+      const selectData = screen.getByTestId("userSelectProxyData")
+      selectData.innerText = JSON.stringify(proxy)
+
+      const selectProxyButton = screen.getByTestId("userSelectProxy")
+      await user.click(selectProxyButton)
+    }
+  }
+
+  it.each([
+    // Not latency behavior
+    [
+      "empty",
+      {
+        expProxyID: "",
+        regions: [],
+        storageProxy: undefined,
+        latencies: {},
+      },
+    ],
+    [
+      "regions_no_selection",
+      {
+        expProxyID: MockPrimaryWorkspaceProxy.id,
+        regions: MockWorkspaceProxies,
+        storageProxy: undefined,
+      },
+    ],
+    [
+      "regions_selected_unhealthy",
+      {
+        expProxyID: MockPrimaryWorkspaceProxy.id,
+        regions: MockWorkspaceProxies,
+        storageProxy: MockUnhealthyWildWorkspaceProxy,
+        expUserProxyID: MockUnhealthyWildWorkspaceProxy.id,
+      },
+    ],
+    [
+      "regions_selected_healthy",
+      {
+        expProxyID: MockHealthyWildWorkspaceProxy.id,
+        regions: MockWorkspaceProxies,
+        storageProxy: MockHealthyWildWorkspaceProxy,
+        expUserProxyID: MockHealthyWildWorkspaceProxy.id,
+      },
+    ],
+    [
+      "regions_selected_clear",
+      {
+        expProxyID: MockPrimaryWorkspaceProxy.id,
+        regions: MockWorkspaceProxies,
+        storageProxy: MockHealthyWildWorkspaceProxy,
+        afterLoad: clearProxyAction,
+        expUserProxyID: undefined,
+      },
+    ],
+    [
+      "regions_make_selection",
+      {
+        expProxyID: MockHealthyWildWorkspaceProxy.id,
+        regions: MockWorkspaceProxies,
+        afterLoad: userSelectProxy(MockHealthyWildWorkspaceProxy),
+        expUserProxyID: MockHealthyWildWorkspaceProxy.id,
+      },
+    ],
+    // Latency behavior
+    [
+      "regions_default_low_latency",
+      {
+        expProxyID: MockHealthyWildWorkspaceProxy.id,
+        regions: MockWorkspaceProxies,
+        storageProxy: undefined,
+        latencies: {
+          [MockPrimaryWorkspaceProxy.id]: fakeLatency(100),
+          [MockHealthyWildWorkspaceProxy.id]: fakeLatency(50),
+          // This is a trick. It's unhealthy so should be ignored.
+          [MockUnhealthyWildWorkspaceProxy.id]: fakeLatency(25),
+        },
+      },
+    ],
+    [
+      // User intentionally selected a high latency proxy.
+      "regions_select_high_latency",
+      {
+        expProxyID: MockHealthyWildWorkspaceProxy.id,
+        regions: MockWorkspaceProxies,
+        storageProxy: undefined,
+        afterLoad: userSelectProxy(MockHealthyWildWorkspaceProxy),
+        expUserProxyID: MockHealthyWildWorkspaceProxy.id,
+        latencies: {
+          [MockHealthyWildWorkspaceProxy.id]: fakeLatency(500),
+          [MockPrimaryWorkspaceProxy.id]: fakeLatency(100),
+          // This is a trick. It's unhealthy so should be ignored.
+          [MockUnhealthyWildWorkspaceProxy.id]: fakeLatency(25),
+        },
+      },
+    ],
+    [
+      // Low latency proxy is selected, but it is unhealthy
+      "regions_select_unhealthy_low_latency",
+      {
+        expProxyID: MockPrimaryWorkspaceProxy.id,
+        regions: MockWorkspaceProxies,
+        storageProxy: MockUnhealthyWildWorkspaceProxy,
+        expUserProxyID: MockUnhealthyWildWorkspaceProxy.id,
+        latencies: {
+          [MockHealthyWildWorkspaceProxy.id]: fakeLatency(500),
+          [MockPrimaryWorkspaceProxy.id]: fakeLatency(100),
+          // This is a trick. It's unhealthy so should be ignored.
+          [MockUnhealthyWildWorkspaceProxy.id]: fakeLatency(25),
+        },
+      },
+    ],
+    [
+      // Excess proxies we do not have are low latency.
+      // This will probably never happen in production.
+      "unknown_regions_low_latency",
+      {
+        // Default to primary since we have unknowns
+        expProxyID: MockPrimaryWorkspaceProxy.id,
+        regions: MockWorkspaceProxies,
+        storageProxy: MockUnhealthyWildWorkspaceProxy,
+        expUserProxyID: MockUnhealthyWildWorkspaceProxy.id,
+        latencies: {
+          ["some"]: fakeLatency(500),
+          ["random"]: fakeLatency(100),
+          ["ids"]: fakeLatency(25),
+        },
+      },
+    ],
+  ] as [string, ProxyContextSelectionTest][])(
+    `%s`,
+    async (
+      _,
+      {
+        expUserProxyID,
+        expProxyID: expSelectedProxyID,
+        regions,
+        storageProxy,
+        latencies = {},
+        afterLoad,
+      },
+    ) => {
+      // Mock the latencies
+      hardCodedLatencies = latencies
+
+      // Initial selection if present
+      if (storageProxy) {
+        saveUserSelectedProxy(storageProxy)
+      }
+
+      // Mock the API response
+      server.use(
+        rest.get("/api/v2/regions", async (req, res, ctx) => {
+          return res(
+            ctx.status(200),
+            ctx.json({
+              regions: regions,
+            }),
+          )
+        }),
+      )
+
+      TestingComponent()
+      await waitForLoaderToBeRemoved()
+
+      if (afterLoad) {
+        await afterLoad()
+      }
+
+      await screen.findByTestId("isFetched").then((x) => {
+        expect(x.title).toBe("true")
+      })
+      await screen.findByTestId("isLoading").then((x) => {
+        expect(x.title).toBe("false")
+      })
+      await screen.findByTestId("preferredProxy").then((x) => {
+        expect(x.title).toBe(expSelectedProxyID)
+      })
+      await screen.findByTestId("userProxy").then((x) => {
+        expect(x.title).toBe(expUserProxyID || "")
+      })
+    },
+  )
+})

site/src/contexts/ProxyContext.tsx

@@ -6,28 +6,60 @@ import {
   createContext,
   FC,
   PropsWithChildren,
+  useCallback,
   useContext,
+  useEffect,
   useState,
 } from "react"
 import { ProxyLatencyReport, useProxyLatency } from "./useProxyLatency"
 
-interface ProxyContextValue {
+export interface ProxyContextValue {
+  // proxy is **always** the workspace proxy that should be used.
+  // The 'proxy.selectedProxy' field is the proxy being used and comes from either:
+  //   1. The user manually selected this proxy. (saved to local storage)
+  //   2. The default proxy auto selected because:
+  //    a. The user has not selected a proxy.
+  //    b. The user's selected proxy is not in the list of proxies.
+  //    c. The user's selected proxy is not healthy.
+  //   3. undefined if there are no proxies.
+  //
+  // The values 'proxy.preferredPathAppURL' and 'proxy.preferredWildcardHostname' can
+  // always be used even if 'proxy.selectedProxy' is undefined. These values are sourced from
+  // the 'selectedProxy', but default to relative paths if the 'selectedProxy' is undefined.
   proxy: PreferredProxy
+
+  // userProxy is always the proxy the user has selected. This value comes from local storage.
+  // The value `proxy` should always be used instead of `userProxy`. `userProxy` is only exposed
+  // so the caller can determine if the proxy being used is the user's selected proxy, or if it
+  // was auto selected based on some other criteria.
+  userProxy?: Region
+
+  // proxies is the list of proxies returned by coderd. This is fetched async.
+  // isFetched, isLoading, and error are used to track the state of the async call.
   proxies?: Region[]
-  proxyLatencies?: Record<string, ProxyLatencyReport>
-  // isfetched is true when the proxy api call is complete.
+  // isFetched is true when the 'proxies' api call is complete.
   isFetched: boolean
-  // isLoading is true if the proxy is in the process of being fetched.
   isLoading: boolean
   error?: Error | unknown
+  // proxyLatencies is a map of proxy id to latency report. If the proxyLatencies[proxy.id] is undefined
+  // then the latency has not been fetched yet. Calculations happen async for each proxy in the list.
+  // Refer to the returned report for a given proxy for more information.
+  proxyLatencies: Record<string, ProxyLatencyReport>
+  // setProxy is a function that sets the user's selected proxy. This function should
+  // only be called if the user is manually selecting a proxy. This value is stored in local
+  // storage and will persist across reloads and tabs.
   setProxy: (selectedProxy: Region) => void
+  // clearProxy is a function that clears the user's selected proxy.
+  // If no proxy is selected, then the default proxy will be used.
+  clearProxy: () => void
 }
 
 interface PreferredProxy {
-  // selectedProxy is the proxy the user has selected.
+  // proxy is the proxy being used. It is provided for
+  // getting the fields such as "display_name" and "id"
   // Do not use the fields 'path_app_url' or 'wildcard_hostname' from this
   // object. Use the preferred fields.
-  selectedProxy: Region | undefined
+  proxy: Region | undefined
   // PreferredPathAppURL is the URL of the proxy or it is the empty string
   // to indicate using relative paths. To add a path to this:
   //  PreferredPathAppURL + "/path/to/app"
@@ -44,19 +76,18 @@ export const ProxyContext = createContext<ProxyContextValue | undefined>(
  * ProxyProvider interacts with local storage to indicate the preferred workspace proxy.
  */
 export const ProxyProvider: FC<PropsWithChildren> = ({ children }) => {
-  // Try to load the preferred proxy from local storage.
-  let savedProxy = loadPreferredProxy()
-  if (!savedProxy) {
-    // If no preferred proxy is saved, then default to using relative paths
-    // and no subdomain support until the proxies are properly loaded.
-    // This is the same as a user not selecting any proxy.
-    savedProxy = getPreferredProxy([])
-  }
-
-  const [proxy, setProxy] = useState<PreferredProxy>(savedProxy)
-
   const dashboard = useDashboard()
   const experimentEnabled = dashboard?.experiments.includes("moons")
+
+  // Using a useState so the caller always has the latest user saved
+  // proxy.
+  const [userSavedProxy, setUserSavedProxy] = useState(loadUserSelectedProxy())
+
+  // Load the initial state from local storage.
+  const [proxy, setProxy] = useState<PreferredProxy>(
+    computeUsableURLS(userSavedProxy),
+  )
+
   const queryKey = ["get-proxies"]
   const {
     data: proxiesResp,
@@ -66,41 +97,37 @@ export const ProxyProvider: FC<PropsWithChildren> = ({ children }) => {
   } = useQuery({
     queryKey,
     queryFn: getWorkspaceProxies,
-    // This onSuccess ensures the local storage is synchronized with the
-    // proxies returned by coderd. If the selected proxy is not in the list,
-    // then the user selection is removed.
-    onSuccess: (resp) => {
-      setAndSaveProxy(proxy.selectedProxy, resp.regions)
-    },
   })
 
-  // Everytime we get a new proxiesResponse, update the latency check
+  // Every time we get a new proxiesResponse, update the latency check
   // to each workspace proxy.
   const proxyLatencies = useProxyLatency(proxiesResp)
 
-  const setAndSaveProxy = (
-    selectedProxy?: Region,
-    // By default the proxies come from the api call above.
-    // Allow the caller to override this if they have a more up
-    // to date list of proxies.
-    proxies: Region[] = proxiesResp?.regions || [],
-  ) => {
-    if (!proxies) {
-      throw new Error(
-        "proxies are not yet loaded, so selecting a proxy makes no sense. How did you get here?",
-      )
-    }
-    const preferred = getPreferredProxy(proxies, selectedProxy)
-    // Save to local storage to persist the user's preference across reloads
-    // and other tabs.
-    savePreferredProxy(preferred)
-    // Set the state for the current context.
-    setProxy(preferred)
-  }
+  // updateProxy is a helper function that when called will
+  // update the proxy being used.
+  const updateProxy = useCallback(() => {
+    // Update the saved user proxy for the caller.
+    setUserSavedProxy(loadUserSelectedProxy())
+    setProxy(
+      getPreferredProxy(
+        proxiesResp?.regions ?? [],
+        loadUserSelectedProxy(),
+        proxyLatencies,
+      ),
+    )
+  }, [proxiesResp, proxyLatencies])
+
+  // This useEffect ensures the proxy to be used is updated whenever the state changes.
+  // This includes proxies being loaded, latencies being calculated, and the user selecting a proxy.
+  useEffect(() => {
+    updateProxy()
+    // eslint-disable-next-line react-hooks/exhaustive-deps -- Only update if the source data changes
+  }, [proxiesResp, proxyLatencies])
 
   return (
     <ProxyContext.Provider
       value={{
+        userProxy: userSavedProxy,
         proxyLatencies: proxyLatencies,
         proxy: experimentEnabled
           ? proxy
@@ -113,9 +140,19 @@ export const ProxyProvider: FC<PropsWithChildren> = ({ children }) => {
         isLoading: proxiesLoading,
         isFetched: proxiesFetched,
         error: proxiesError,
-        // A function that takes the new proxies and selected proxy and updates
-        // the state with the appropriate urls.
-        setProxy: setAndSaveProxy,
+
+        // These functions are exposed to allow the user to select a proxy.
+        setProxy: (proxy: Region) => {
+          // Save to local storage to persist the user's preference across reloads
+          saveUserSelectedProxy(proxy)
+          // Update the selected proxy
+          updateProxy()
+        },
+        clearProxy: () => {
+          // Clear the user's selection from local storage.
+          clearUserSelectedProxy()
+          updateProxy()
+        },
       }}
     >
       {children}
@@ -134,22 +171,20 @@ export const useProxy = (): ProxyContextValue => {
 }
 
 /**
- * getURLs is a helper function to calculate the urls to use for a given proxy configuration. By default, it is
+ * getPreferredProxy is a helper function to calculate the urls to use for a given proxy configuration. By default, it is
  * assumed no proxy is configured and relative paths should be used.
  * Exported for testing.
  *
  * @param proxies Is the list of proxies returned by coderd. If this is empty, default behavior is used.
- * @param selectedProxy Is the proxy the user has selected. If this is undefined, default behavior is used.
+ * @param selectedProxy Is the proxy saved in local storage. If this is undefined, default behavior is used.
+ * @param latencies If provided, this is used to determine the best proxy to default to.
+ *                  If not, `primary` is always the best default.
  */
 export const getPreferredProxy = (
   proxies: Region[],
   selectedProxy?: Region,
+  latencies?: Record<string, ProxyLatencyReport>,
 ): PreferredProxy => {
-  // By default we set the path app to relative and disable wildcard hostnames.
-  // We will set these values if we find a proxy we can use that supports them.
-  let pathAppURL = ""
-  let wildcardHostname = ""
-
   // If a proxy is selected, make sure it is in the list of proxies. If it is not
   // we should default to the primary.
   selectedProxy = proxies.find(
@@ -158,37 +193,76 @@ export const getPreferredProxy = (
 
   // If no proxy is selected, or the selected proxy is unhealthy default to the primary proxy.
   if (!selectedProxy || !selectedProxy.healthy) {
+    // By default, use the primary proxy.
     selectedProxy = proxies.find((proxy) => proxy.name === "primary")
+    // If we have latencies, then attempt to use the best proxy by latency instead.
+    if (latencies) {
+      const proxyMap = proxies.reduce((acc, proxy) => {
+        acc[proxy.id] = proxy
+        return acc
+      }, {} as Record<string, Region>)
+
+      const best = Object.keys(latencies)
+        .map((proxyId) => {
+          return {
+            id: proxyId,
+            ...latencies[proxyId],
+          }
+        })
+        // If the proxy is not in our list, or it is unhealthy, ignore it.
+        .filter((latency) => proxyMap[latency.id]?.healthy)
+        .sort((a, b) => a.latencyMS - b.latencyMS)
+        .at(0)
+
+      // Found a new best, use it!
+      if (best) {
+        const bestProxy = proxies.find((proxy) => proxy.id === best.id)
+        // Default to w/e it was before
+        selectedProxy = bestProxy || selectedProxy
+      }
+    }
   }
 
-  // Only use healthy proxies.
-  if (selectedProxy && selectedProxy.healthy) {
+  return computeUsableURLS(selectedProxy)
+}
+
+const computeUsableURLS = (proxy?: Region): PreferredProxy => {
+  if (!proxy) {
     // By default use relative links for the primary proxy.
     // This is the default, and we should not change it.
-    if (selectedProxy.name !== "primary") {
-      pathAppURL = selectedProxy.path_app_url
+    return {
+      proxy: undefined,
+      preferredPathAppURL: "",
+      preferredWildcardHostname: "",
     }
-    wildcardHostname = selectedProxy.wildcard_hostname
   }
 
-  // TODO: @emyrk Should we notify the user if they had an unhealthy proxy selected?
+  let pathAppURL = proxy?.path_app_url.replace(/\/$/, "")
+  // Primary proxy uses relative paths. It's the only exception.
+  if (proxy.name === "primary") {
+    pathAppURL = ""
+  }
 
   return {
-    selectedProxy: selectedProxy,
+    proxy: proxy,
     // Trim trailing slashes to be consistent
-    preferredPathAppURL: pathAppURL.replace(/\/$/, ""),
-    preferredWildcardHostname: wildcardHostname,
+    preferredPathAppURL: pathAppURL,
+    preferredWildcardHostname: proxy.wildcard_hostname,
   }
 }
 
 // Local storage functions
 
-export const savePreferredProxy = (saved: PreferredProxy): void => {
-  window.localStorage.setItem("preferred-proxy", JSON.stringify(saved))
+export const clearUserSelectedProxy = (): void => {
+  window.localStorage.removeItem("user-selected-proxy")
 }
 
-const loadPreferredProxy = (): PreferredProxy | undefined => {
-  const str = localStorage.getItem("preferred-proxy")
+export const saveUserSelectedProxy = (saved: Region): void => {
+  window.localStorage.setItem("user-selected-proxy", JSON.stringify(saved))
+}
+
+export const loadUserSelectedProxy = (): Region | undefined => {
+  const str = localStorage.getItem("user-selected-proxy")
   if (!str) {
     return undefined
   }

site/src/pages/TerminalPage/TerminalPage.test.tsx

@@ -46,7 +46,7 @@ const renderTerminal = () => {
             value={{
               proxyLatencies: MockProxyLatencies,
               proxy: {
-                selectedProxy: MockPrimaryWorkspaceProxy,
+                proxy: MockPrimaryWorkspaceProxy,
                 preferredPathAppURL: "",
                 preferredWildcardHostname: "",
               },
@@ -54,6 +54,7 @@ const renderTerminal = () => {
               isFetched: true,
               isLoading: false,
               setProxy: jest.fn(),
+              clearProxy: jest.fn(),
             }}
           >
             <TerminalPage renderer="dom" />

site/src/pages/UserSettingsPage/WorkspaceProxyPage/WorkspaceProxyPage.tsx

@@ -36,7 +36,7 @@ export const WorkspaceProxyPage: FC<PropsWithChildren<unknown>> = () => {
         isLoading={proxiesLoading}
         hasLoaded={proxiesFetched}
         getWorkspaceProxiesError={proxiesError}
-        preferredProxy={proxy.selectedProxy}
+        preferredProxy={proxy.proxy}
         onSelect={(proxy) => {
           if (!proxy.healthy) {
             displayError("Please select a healthy workspace proxy.")

site/src/testHelpers/entities.ts

@@ -1397,7 +1397,10 @@ export const MockEntitlementsWithScheduling: TypesGen.Entitlements = {
   }),
 }
 
-export const MockExperiments: TypesGen.Experiment[] = ["workspace_actions"]
+export const MockExperiments: TypesGen.Experiment[] = [
+  "workspace_actions",
+  "moons",
+]
 
 export const MockAuditLog: TypesGen.AuditLog = {
   id: "fbd2116a-8961-4954-87ae-e4575bd29ce0",

site/src/testHelpers/localstorage.ts

@@ -0,0 +1,22 @@
+export const localStorageMock = () => {
+  const store = {} as Record<string, string>
+
+  return {
+    getItem: (key: string): string => {
+      return store[key]
+    },
+    setItem: (key: string, value: string) => {
+      store[key] = value
+    },
+    clear: () => {
+      Object.keys(store).forEach((key) => {
+        delete store[key]
+      })
+    },
+    removeItem: (key: string) => {
+      delete store[key]
+    },
+  }
+}
+
+Object.defineProperty(window, "localStorage", { value: localStorageMock() })